From owner-chemistry@ccl.net Fri Jun 9 03:14:01 2006 From: "Andreas Klamt klamt(0)cosmologic.de" To: CCL Subject: CCL:G: PCM on a torus Message-Id: <-31915-060609023313-15249-FjJ2M1qLJpJfyk9W+9Suhg**server.ccl.net> X-Original-From: Andreas Klamt Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-15 Date: Fri, 09 Jun 2006 08:32:50 +0200 MIME-Version: 1.0 Sent to CCL by: Andreas Klamt [klamt[#]cosmologic.de] Hi Steve, there is no problem with such molecules within my COSMO cavity constructions, e.g. in TURBOMOLE. Indeed, checking that this morning led me to a nice picture of the screening charge density on 18-crown-6-ether, which you can see as a jpg on our homepage under www.cosmologic.de/18-crown-6-ether.jpg or www.cosmologic.de/18-crown-6-ether.wrz (as a zipped VRML file) (the VRML files are generated with COSMOtherm and the jpg screenshot is > from the CORTONA VRML viewer.) Regards Andreas Steven Bachrach sbachrach+/-trinity.edu schrieb: > Sent to CCL by: "Steven Bachrach" [sbachrach_+_trinity.edu] > I would like to perform solvation calculations on a molecule that is a torus (i.e., a doughnut or bagel shape). A PCM calculation using Gaussian-03 failed when constructing the cavity, with an error message: > > AdVTs1: ISph= 454 is engulfed by JSph= 489 but Ae( 454) is not yet zero! > > I am thinking that the problem is that the topology of the necessary cavity is a doughnut (torus), but PCM usesa cavity that must be topologically related to the sphere. Am I correct in this? Is there some way to do this type of computation? (One idea I have is to place a few explicit solvent molecules in the interior, filling it up, thereby removing the hole so the cavity can then be of spherical topology.) > > Thanks, > > Steve Bachrach > > -- > Steven Bachrach ph: (210)999-7379 > Department of Chemistry fax: (210)999-7569 > Trinity University > 1 Trinity Place > San Antonio, TX 78212 > steven.bachrach(!)trinity.edu> > > > > > -- ----------------------------------------------------------------------------- Dr. habil. Andreas Klamt COSMOlogic GmbH&CoKG Burscheider Str. 515 51381 Leverkusen, Germany Tel.: +49-2171-73168-1 Fax: +49-2171-73168-9 e-mail: klamt.**.cosmologic.de web: www.cosmologic.de ----------------------------------------------------------------------------- COSMOlogic Your Competent Partner for Computational Chemistry and Fluid Thermodynamics ----------------------------------------------------------------------------- From owner-chemistry@ccl.net Fri Jun 9 09:18:01 2006 From: "Ulrike Salzner salzner-*-fen.bilkent.edu.tr" To: CCL Subject: CCL:G: relative signs of orbitals in alpha and beta orbital space Message-Id: <-31916-060609081618-18254-03mAG6gF/d1xZLt3CHWgYQ###server.ccl.net> X-Original-From: Ulrike Salzner Content-Transfer-Encoding: 7bit Content-Type: text/plain Date: Fri, 09 Jun 2006 14:28:09 +0300 Mime-Version: 1.0 Sent to CCL by: Ulrike Salzner [salzner(~)fen.bilkent.edu.tr] Dear collegues, are the relative signs of alpha and beta orbitasl in an open-shell calculation fixed or random? Consider for instance the octatetraene cation. Since one electron is removed, HOMO alpha and LUMO beta have the same nodal structure. HOMO alpha is a pi-orbital with the following signs of the p-orbital coefficients: ++,--,++,--. Is there a difference if the beta LUMO orbital starts also with plus or with minus like: --,++,--,++. The reason why I am wondering about this is that I am doing TDDFT excited state calculations on polyenes. The first allowed excited state is composed mainly of one-electron HOMO-LUMO transitions in alpha and beta spaces. According to CASSCF and CASPT2 calculations the two transitions mix with opposite signs to create a dipole allowed state and with same sign to produce a dipole forbidden state. With TDDFT I can reproduce excitation energies and oscillator strength well but the usually the two excitations mix with same signs to produce the dipole allowed state. In several cases the signs are opposite, however. Inspecting the orbitals showed that in same sign cases the beta LUMO is the mirror image of the alpha HOMO. In opposite sign cases alpha HOMO and alpha LUMO start with the same sign of the coefficients. Thus, if the relative signs of alpha and beta orbitals are random, it makes sense that the signs are sometimes same and somtimes different. If they are not, I have a problem to understand what is going on. Does anyone know more about this? I do not think that this has to do with the program I am using, but it is the much discussed G03. Thanks in advance for comments, Ulrike -- Ulrike Salzner Associate Professor Department of Chemistry Bilkent University 06800 Bilkent, Ankara Turkey From owner-chemistry@ccl.net Fri Jun 9 09:52:03 2006 From: "Van Dam, HJJ \(Huub\) h.j.j.vandam/./dl.ac.uk" To: CCL Subject: CCL:G: relative signs of orbitals in alpha and beta orbital space Message-Id: <-31917-060609094525-12013-jJCu1/Z9yuXjR/b1m2LMug^server.ccl.net> X-Original-From: "Van Dam, HJJ \(Huub\)" Content-Class: urn:content-classes:message Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" Date: Fri, 9 Jun 2006 14:45:20 +0100 MIME-Version: 1.0 Sent to CCL by: "Van Dam, HJJ \(Huub\)" [h.j.j.vandam .. dl.ac.uk] Hi Ulrike, The orbital is the solution of an eigenvalue equation (it does not matter if it is a generalized eigenvalue equation or not). If a vector X is a solution of the eigenvalue equation then A*X is also a solution of the eigenvalue equation with the same eigenvalue (effectively you are only scaling the whole equation with a factor A, a neat way by which this is usually exploited is by normalising your eigenvectors). Anyway as you will realize by now there is nothing stopping you from chosing A to be -1. Although the sign of an orbital is physically insignificant you have spotted quite well that this can be very annoying when you try to compare results. In various debugging sessions this has proven to be a real pain. Sofar I have not found a rigorous way to fix the sign of an orbital (choosing the sum of all elements to be positive, choosing the component with the maximum absolute value to be positive, etc. all fail occassionally). So if anyone has some clever ideas about this I would be keen to know. Best wishes, Huub ========================================================== Huub van Dam (h.j.j.vandam__dl.ac.uk, +44-1925-603933) ========================================================== -----Original Message----- > From: owner-chemistry__ccl.net [mailto:owner-chemistry__ccl.net] Sent: 09 June 2006 14:23 To: Vandam, Huub Subject: CCL:G: relative signs of orbitals in alpha and beta orbital space Sent to CCL by: Ulrike Salzner [salzner(~)fen.bilkent.edu.tr] Dear collegues, are the relative signs of alpha and beta orbitasl in an open-shell calculation fixed or random? Consider for instance the octatetraene cation. Since one electron is removed, HOMO alpha and LUMO beta have the same nodal structure. HOMO alpha is a pi-orbital with the following signs of the p-orbital coefficients: ++,--,++,--. Is there a difference if the beta LUMO orbital starts also with plus or with minus like: --,++,--,++. The reason why I am wondering about this is that I am doing TDDFT excited state calculations on polyenes. The first allowed excited state is composed mainly of one-electron HOMO-LUMO transitions in alpha and beta spaces. According to CASSCF and CASPT2 calculations the two transitions mix with opposite signs to create a dipole allowed state and with same sign to produce a dipole forbidden state. With TDDFT I can reproduce excitation energies and oscillator strength well but the usually the two excitations mix with same signs to produce the dipole allowed state. In several cases the signs are opposite, however. Inspecting the orbitals showed that in same sign cases the beta LUMO is the mirror image of the alpha HOMO. In opposite sign cases alpha HOMO and alpha LUMO start with the same sign of the coefficients. Thus, if the relative signs of alpha and beta orbitals are random, it makes sense that the signs are sometimes same and somtimes different. If they are not, I have a problem to understand what is going on. Does anyone know more about this? I do not think that this has to do with the program I am using, but it is the much discussed G03. Thanks in advance for comments, Ulrike -- Ulrike Salzner Associate Professor Department of Chemistry Bilkent University 06800 Bilkent, Ankara Turkeyhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt From owner-chemistry@ccl.net Fri Jun 9 10:38:05 2006 From: "Fernando D. Vila fer---phys.washington.edu" To: CCL Subject: CCL: UFF Energy/Forces/Hessian implementation Message-Id: <-31918-060608204505-585-eFlu6LBm7LPdrndBuUhQ5w#,#server.ccl.net> X-Original-From: "Fernando D. Vila" Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Date: Thu, 8 Jun 2006 17:02:32 -0700 (PDT) MIME-Version: 1.0 Sent to CCL by: "Fernando D. Vila" [fer|phys.washington.edu] Hello everyone; I'm looking for an implementation of the UFF Hessian that I can link to > from a code I'm working on. I could also do with an implementation that has only energies or forces, I just don't want to go through all the literature digging out the equations and parameters. Thanks in advance, Fer. Ubi dubium ibi libertas. ******************************************************************************* Fernando D. Vila Voice (206)543-9697 Department of Physics Fax (206)685-0635 University of Washington E-mail fdv^^^u.washington.edu Seattle, WA 98195, USA WWW http://faculty.washington.edu/fdv ******************************************************************************* From owner-chemistry@ccl.net Fri Jun 9 11:13:00 2006 From: "Georg Lefkidis lefkidis%x%physik.uni-kl.de" To: CCL Subject: CCL:G: AW: G: relative signs of orbitals in alpha and beta orbital space Message-Id: <-31919-060609104433-21127-61ExEcgEI6Yy2M6+alOZKA-*-server.ccl.net> X-Original-From: "Georg Lefkidis" Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="iso-8859-1" Date: Fri, 9 Jun 2006 16:44:08 +0200 MIME-Version: 1.0 Sent to CCL by: "Georg Lefkidis" [lefkidis:+:physik.uni-kl.de] Hi, the sign of the orbitals is really arbitrary. If you have three atomic orbitals basis then it is the same problem like in 3D mechanics choosing between a left or a right handed system. With more orbitals it gets more generalized. Unfortunately there is no way to tell in advance the relative signs, since the molecular orbitals are orthogonal, and in principle there is no difference-it is nothing more than an artefact of the diagonalization procedure. This appears very clearly for example in optical problems. To my knowledge, the only think one can compare is the absolute value (or square if real wavefunctions are used) of the orbitals. In principle the degree of the arbitrariness is the dimensionality of the space, in other words every AO adds a sign ambiguity.Even the slightest numerical difference can lead to jumps from negative to positive values, a fact however that should not appear in any observable, e.g. transition probabilities or densities (the problem becomes even more complicated if complex wavefunctions come into play, and then only the absolute values can be compared. This is quite often frustrating indeed, but I believe that there is no way around, it's an innate problem of orthogonal basis sets). The only thing that comes to my mind is to make the largest coefficient of EVERY molecular orbital positive (or negative) which will of course work only if there are not equally large components with opposite site (which unfortunately is the case if e.g. one builds open shell singlets, where there are always to determinants with equal coefficents and opposite signs, and chosing the one over the other is arbitrary as well. Cheers Georg > -----Ursprüngliche Nachricht----- > Von: owner-chemistry|ccl.net [mailto:owner-chemistry|ccl.net] > Gesendet: Freitag, 9. Juni 2006 16:10 > An: Lefkidis, Georg > Betreff: CCL:G: relative signs of orbitals in alpha and beta orbital > space > > > Sent to CCL by: "Van Dam, HJJ \(Huub\)" [h.j.j.vandam .. dl.ac.uk] > Hi Ulrike, > > The orbital is the solution of an eigenvalue equation (it does not > matter if it is a generalized eigenvalue equation or not). If a vector X > is a solution of the eigenvalue equation then A*X is also a solution of > the eigenvalue equation with the same eigenvalue (effectively you are > only scaling the whole equation with a factor A, a neat way by which > this is usually exploited is by normalising your eigenvectors). Anyway > as you will realize by now there is nothing stopping you from chosing A > to be -1. > > Although the sign of an orbital is physically insignificant you have > spotted quite well that this can be very annoying when you try to > compare results. In various debugging sessions this has proven to be a > real pain. Sofar I have not found a rigorous way to fix the sign of an > orbital (choosing the sum of all elements to be positive, choosing the > component with the maximum absolute value to be positive, etc. all fail > occassionally). So if anyone has some clever ideas about this I would be > keen to know. > > Best wishes, > > Huub > > > ========================================================== > Huub van Dam (h.j.j.vandam(-)dl.ac.uk, +44-1925-603933) > ========================================================== > > > -----Original Message----- > > From: owner-chemistry(-)ccl.net [mailto:owner-chemistry(-)ccl.net] > Sent: 09 June 2006 14:23 > To: Vandam, Huub > Subject: CCL:G: relative signs of orbitals in alpha and beta orbital > space > > Sent to CCL by: Ulrike Salzner [salzner(~)fen.bilkent.edu.tr] Dear > collegues, are the relative signs of alpha and beta orbitasl in an > open-shell calculation fixed or random? > > Consider for instance the octatetraene cation. Since one electron is > removed, HOMO alpha and LUMO beta have the same nodal structure. HOMO > alpha is a pi-orbital with the following signs of the p-orbital > coefficients: ++,--,++,--. Is there a difference if the beta LUMO > orbital starts also with plus or with minus like: --,++,--,++. > > The reason why I am wondering about this is that I am doing TDDFT > excited state calculations on polyenes. The first allowed excited state > is composed mainly of one-electron HOMO-LUMO transitions in alpha and > beta spaces. According to CASSCF and CASPT2 calculations the two > transitions mix with opposite signs to create a dipole allowed state and > with same sign to produce a dipole forbidden state. > > With TDDFT I can reproduce excitation energies and oscillator strength > well but the usually the two excitations mix with same signs to produce > the dipole allowed state. In several cases the signs are opposite, > however. Inspecting the orbitals showed that in same sign cases the beta > LUMO is the mirror image of the alpha HOMO. In opposite sign cases alpha > HOMO and alpha LUMO start with the same sign of the coefficients. Thus, > if the relative signs of alpha and beta orbitals are random, it makes > sense that the signs are sometimes same and somtimes different. If they > are not, I have a problem to understand what is going on. > > Does anyone know more about this? I do not think that this has to do > with the program I am using, but it is the much discussed G03. > > Thanks in advance for comments, > Ulrike > -- > Ulrike Salzner > Associate Professor > Department of Chemistry > Bilkent University > 06800 Bilkent, Ankara > Turkeyhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.cc > l.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt> > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.394 / Virus Database: 268.8.3/359 - Release Date: 08/06/06 > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.8.3/359 - Release Date: 08/06/06 From owner-chemistry@ccl.net Fri Jun 9 12:42:00 2006 From: "T. Daniel Crawford crawdad]^[exchange.vt.edu" To: CCL Subject: CCL:G: relative signs of orbitals in alpha and beta orbital space Message-Id: <-31920-060609124005-12301-srxlf36j4ks5FWNxgT1EGA^^^server.ccl.net> X-Original-From: "T. Daniel Crawford" Content-transfer-encoding: 7bit Content-type: text/plain; charset="US-ASCII" Date: Fri, 09 Jun 2006 11:52:55 -0400 Mime-version: 1.0 Sent to CCL by: "T. Daniel Crawford" [crawdad.]^[.exchange.vt.edu] Dear Huub, I agree that the arbitrariness of the phase/sign of the molecular orbitals can be a frustration, particularly for debugging. It's also problematic in calculations involving correlated wave functions, e.g., coupled cluster, where one would like to use a previous wave function as an initial guess for a new calculation. In a geometry optimization, for example, the phases on the MOs can change, which means that individual components of the old correlated wave function (expressed in the MO basis) will have signs that don't match the new MO-basis integrals. But here's a trick that might be useful to you to maintain a particular choice of phase/sign of the MOs in such cases. Keep a copy of the original MOs (from the previous geometry, for example), and, after you've computed the new MOs compute the approximate identity: I ~= C+_old S C_new where the "+: denotes transposition, and C_old and C_new are the old and new SCF eigenvector matrices, respectively. If the two MO sets are a little different, as they would be between geometry optimization cycles, the matrix, I, on the left-hand side would have values of nearly 1.0 along the diagonal -- except for those columns of C_old and C_new where the phases differ, when the diagonal element is approximately -1.0. So, all you have to do is scan the diagonal elements of I and, if you find a -1, multiply that entire column of C_new by -1 to "fix" its phase to match that of C_old. Then you'll be able to re-use the old correlated wave function for restarting the calculation. If the C_old and C_new differ more substantially, e.g. if the MOs change their energetic ordering between steps, then the I matrix will have rows/columns for which the largest elements will off the diagonal. You can either swap the column ordering in C_new to match C_old, or, more safely, set a flag to prevent a restart from the old correlated wave function. We do this in the PSI3 package, for example, and it works well for ground-state wave functions, perturbed wave functions, etc. -Daniel P.S. Credit where credit is due: I believe this idea originally came from Tim Lee (NASA Ames), and I learned it from Tracy Hamilton (UAB). On 6/9/06 10:25 AM, "Van Dam, HJJ (Huub) h.j.j.vandam/./dl.ac.uk" wrote: > Sent to CCL by: "Van Dam, HJJ \(Huub\)" [h.j.j.vandam .. dl.ac.uk] > Hi Ulrike, > > The orbital is the solution of an eigenvalue equation (it does not > matter if it is a generalized eigenvalue equation or not). If a vector X > is a solution of the eigenvalue equation then A*X is also a solution of > the eigenvalue equation with the same eigenvalue (effectively you are > only scaling the whole equation with a factor A, a neat way by which > this is usually exploited is by normalising your eigenvectors). Anyway > as you will realize by now there is nothing stopping you from chosing A > to be -1. > > Although the sign of an orbital is physically insignificant you have > spotted quite well that this can be very annoying when you try to > compare results. In various debugging sessions this has proven to be a > real pain. Sofar I have not found a rigorous way to fix the sign of an > orbital (choosing the sum of all elements to be positive, choosing the > component with the maximum absolute value to be positive, etc. all fail > occassionally). So if anyone has some clever ideas about this I would be > keen to know. > > Best wishes, > > Huub > > > ========================================================== > Huub van Dam (h.j.j.vandam(-)dl.ac.uk, +44-1925-603933) > ========================================================== > > > -----Original Message----- >> From: owner-chemistry(-)ccl.net [mailto:owner-chemistry(-)ccl.net] > Sent: 09 June 2006 14:23 > To: Vandam, Huub > Subject: CCL:G: relative signs of orbitals in alpha and beta orbital > space > > Sent to CCL by: Ulrike Salzner [salzner(~)fen.bilkent.edu.tr] Dear > collegues, are the relative signs of alpha and beta orbitasl in an > open-shell calculation fixed or random? > > Consider for instance the octatetraene cation. Since one electron is > removed, HOMO alpha and LUMO beta have the same nodal structure. HOMO > alpha is a pi-orbital with the following signs of the p-orbital > coefficients: ++,--,++,--. Is there a difference if the beta LUMO > orbital starts also with plus or with minus like: --,++,--,++. > > The reason why I am wondering about this is that I am doing TDDFT > excited state calculations on polyenes. The first allowed excited state > is composed mainly of one-electron HOMO-LUMO transitions in alpha and > beta spaces. According to CASSCF and CASPT2 calculations the two > transitions mix with opposite signs to create a dipole allowed state and > with same sign to produce a dipole forbidden state. > > With TDDFT I can reproduce excitation energies and oscillator strength > well but the usually the two excitations mix with same signs to produce > the dipole allowed state. In several cases the signs are opposite, > however. Inspecting the orbitals showed that in same sign cases the beta > LUMO is the mirror image of the alpha HOMO. In opposite sign cases alpha > HOMO and alpha LUMO start with the same sign of the coefficients. Thus, > if the relative signs of alpha and beta orbitals are random, it makes > sense that the signs are sometimes same and somtimes different. If they > are not, I have a problem to understand what is going on. > > Does anyone know more about this? I do not think that this has to do > with the program I am using, but it is the much discussed G03. > > Thanks in advance for comments, > Ulrike > -- > Ulrike Salzner > Associate Professor > Department of Chemistry > Bilkent University > 06800 Bilkent, Ankara > Turkeyhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemis > try/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt> > > -- T. Daniel Crawford Department of Chemistry crawdad]^[vt.edu Virginia Tech www.chem.vt.edu/faculty/crawford.php Voice: 540-231-7760 FAX: 540-231-3255 -------------------- PGP Public Key at: http://www.chem.vt.edu/chem-dept/crawford/publickey.txt From owner-chemistry@ccl.net Fri Jun 9 13:23:02 2006 From: "Jim Kress ccl_nospam|kressworks.com" To: CCL Subject: CCL: UFF Energy/Forces/Hessian implementation Message-Id: <-31921-060609123832-11999-03mAG6gF/d1xZLt3CHWgYQ()server.ccl.net> X-Original-From: "Jim Kress" Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii" Date: Fri, 9 Jun 2006 12:38:19 -0400 MIME-Version: 1.0 Sent to CCL by: "Jim Kress" [ccl_nospam_-_kressworks.com] Try Towhee http://towhee.sourceforge.net/ Jim > -----Original Message----- > From: Fernando D. Vila fer---phys.washington.edu > [mailto:owner-chemistry^ccl.net] > Sent: Friday, June 09, 2006 10:40 AM > To: Kress, Jim > Subject: CCL: UFF Energy/Forces/Hessian implementation > > Sent to CCL by: "Fernando D. Vila" [fer|phys.washington.edu] > Hello everyone; > > I'm looking for an implementation of the UFF Hessian that > I can link to > > from a code I'm working on. I could also do with an implementation > > that > has only energies or forces, I just don't want to go through > all the literature digging out the equations and parameters. > > Thanks in advance, Fer. > > Ubi dubium ibi libertas. > ************************************************************** > ***************** > Fernando D. Vila Voice (206)543-9697 > Department of Physics Fax (206)685-0635 > University of Washington E-mail fdv ~~ u.washington.edu > Seattle, WA 98195, USA WWW > http://faculty.washington.edu/fdv > ************************************************************** > ***************** > > > > -= This is automatically added to each message by the mailing > script =- To recover the email address of the author of the > message, please change the strange characters on the top line > to the ^ sign. You can also look up the X-Original-From: line > in the mail header.> Conferences: > http://server.ccl.net/chemistry/announcements/conferences/ > > Search Messages: http://www.ccl.net/htdig (login: ccl, > Password: search)> > -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > -+-+-+-+-+ > > > > > From owner-chemistry@ccl.net Fri Jun 9 21:05:01 2006 From: "Igor Schweigert ischweig|-|uci.edu" To: CCL Subject: CCL:G: relative signs of orbitals in alpha and beta orbital space Message-Id: <-31922-060609113309-29445-T5kqwylpXFWd1vtNbbRIvg]~[server.ccl.net> X-Original-From: "Igor Schweigert" Content-Type: multipart/alternative; boundary="----=_Part_23461_21515299.1149867180229" Date: Fri, 9 Jun 2006 08:33:00 -0700 MIME-Version: 1.0 Sent to CCL by: "Igor Schweigert" [ischweig*o*uci.edu] ------=_Part_23461_21515299.1149867180229 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline As the previous post said, it is implementation-dependent. AFAK, some naive codes would have it the way the eigensolver returns (ie random?), some will choose the sign so that the largest AO coefficient is positive, others will do something else... On the other hand, although I may not quite understood your situation, but the sign of the linear combination of determinants is uniquely defined by the antisymmetry of the total wavefunction. Although UHF is symmetry-broken, but if you took an RHF solution, and manually changed the sign of the beta orbitals, then the linear combination would have a different sign, because when you permute alpha and beta electron you now get an extra sign change. You may have to do the algebra to verify it. Hope this helps, Igor On 6/9/06, Van Dam, HJJ (Huub) h.j.j.vandam/./dl.ac.uk < owner-chemistry^-^ccl.net> wrote: > > Sent to CCL by: "Van Dam, HJJ \(Huub\)" [h.j.j.vandam .. dl.ac.uk] > Hi Ulrike, > > The orbital is the solution of an eigenvalue equation (it does not > matter if it is a generalized eigenvalue equation or not). If a vector X > is a solution of the eigenvalue equation then A*X is also a solution of > the eigenvalue equation with the same eigenvalue (effectively you are > only scaling the whole equation with a factor A, a neat way by which > this is usually exploited is by normalising your eigenvectors). Anyway > as you will realize by now there is nothing stopping you from chosing A > to be -1. > > Although the sign of an orbital is physically insignificant you have > spotted quite well that this can be very annoying when you try to > compare results. In various debugging sessions this has proven to be a > real pain. Sofar I have not found a rigorous way to fix the sign of an > orbital (choosing the sum of all elements to be positive, choosing the > component with the maximum absolute value to be positive, etc. all fail > occassionally). So if anyone has some clever ideas about this I would be > keen to know. > > Best wishes, > > Huub > > > ========================================================== > Huub van Dam (h.j.j.vandam(-)dl.ac.uk, +44-1925-603933) > ========================================================== > > > -----Original Message----- > > From: owner-chemistry(-)ccl.net [mailto:owner-chemistry(-)ccl.net] > Sent: 09 June 2006 14:23 > To: Vandam, Huub > Subject: CCL:G: relative signs of orbitals in alpha and beta orbital > space > > Sent to CCL by: Ulrike Salzner [salzner(~)fen.bilkent.edu.tr] Dear > collegues, are the relative signs of alpha and beta orbitasl in an > open-shell calculation fixed or random? > > Consider for instance the octatetraene cation. Since one electron is > removed, HOMO alpha and LUMO beta have the same nodal structure. HOMO > alpha is a pi-orbital with the following signs of the p-orbital > coefficients: ++,--,++,--. Is there a difference if the beta LUMO > orbital starts also with plus or with minus like: --,++,--,++. > > The reason why I am wondering about this is that I am doing TDDFT > excited state calculations on polyenes. The first allowed excited state > is composed mainly of one-electron HOMO-LUMO transitions in alpha and > beta spaces. According to CASSCF and CASPT2 calculations the two > transitions mix with opposite signs to create a dipole allowed state and > with same sign to produce a dipole forbidden state. > > With TDDFT I can reproduce excitation energies and oscillator strength > well but the usually the two excitations mix with same signs to produce > the dipole allowed state. In several cases the signs are opposite, > however. Inspecting the orbitals showed that in same sign cases the beta > LUMO is the mirror image of the alpha HOMO. In opposite sign cases alpha > HOMO and alpha LUMO start with the same sign of the coefficients. Thus, > if the relative signs of alpha and beta orbitals are random, it makes > sense that the signs are sometimes same and somtimes different. If they > are not, I have a problem to understand what is going on. > > Does anyone know more about this? I do not think that this has to do > with the program I am using, but it is the much discussed G03. > > Thanks in advance for comments, > Ulrike > -- > Ulrike Salzner > Associate Professor > Department of Chemistry > Bilkent University > 06800 Bilkent, Ankara > > Turkeyhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt> > > > ------=_Part_23461_21515299.1149867180229 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline As the previous post said, it is implementation-dependent. AFAK, some naive codes would have it the way the eigensolver returns (ie random?), some will choose the sign so that the largest AO coefficient is positive, others will do something else...

On the other hand, although I may not quite understood your situation, but the sign of the linear combination of determinants is uniquely defined by the antisymmetry of the total wavefunction. Although UHF is symmetry-broken, but if you took an RHF solution, and manually changed the sign of the beta orbitals, then the linear combination would have a different sign, because when you permute alpha and beta electron you now get an extra sign change. You may have to do the algebra to verify it.

Hope this helps,
Igor


On 6/9/06, Van Dam, HJJ (Huub) h.j.j.vandam/./dl.ac.uk <owner-chemistry^-^ccl.net> wrote:
Sent to CCL by: "Van Dam, HJJ \(Huub\)" [h.j.j.vandam .. dl.ac.uk]
Hi Ulrike,

The orbital is the solution of an eigenvalue equation (it does not
matter if it is a generalized eigenvalue equation or not). If a vector X
is a solution of the eigenvalue equation then A*X is also a solution of
the eigenvalue equation with the same eigenvalue (effectively you are
only scaling the whole equation with a factor A, a neat way by which
this is usually exploited is by normalising your eigenvectors). Anyway
as you will realize by now there is nothing stopping you from chosing A
to be -1.

Although the sign of an orbital is physically insignificant you have
spotted quite well that this can be very annoying when you try to
compare results. In various debugging sessions this has proven to be a
real pain. Sofar I have not found a rigorous way to fix the sign of an
orbital (choosing the sum of all elements to be positive, choosing the
component with the maximum absolute value to be positive, etc. all fail
occassionally). So if anyone has some clever ideas about this I would be
keen to know.

Best wishes,

    Huub


==========================================================
Huub van Dam (h.j.j.vandam(-)dl.ac.uk, +44-1925-603933)
==========================================================


-----Original Message-----
> From: owner-chemistry(-)ccl.net [mailto:owner-chemistry(-)ccl.net]
Sent: 09 June 2006 14:23
To: Vandam, Huub
Subject: CCL:G: relative signs of orbitals in alpha and beta orbital
space

Sent to CCL by: Ulrike Salzner [salzner(~)fen.bilkent.edu.tr] Dear
collegues, are the relative signs of alpha and beta orbitasl in an
open-shell calculation fixed or random?

Consider for instance the octatetraene cation. Since one electron is
removed, HOMO alpha and LUMO beta have the same nodal structure. HOMO
alpha is a pi-orbital with the following signs of the p-orbital
coefficients: ++,--,++,--. Is there a difference if the beta LUMO
orbital starts also with plus or with minus like: --,++,--,++.

The reason why I am wondering about this is that I am doing TDDFT
excited state calculations on polyenes. The first allowed excited state
is composed mainly of one-electron HOMO-LUMO transitions in alpha and
beta spaces. According to CASSCF and CASPT2 calculations the two
transitions mix with opposite signs to create a dipole allowed state and
with same sign to produce a dipole forbidden state.

With TDDFT I can reproduce excitation energies and oscillator strength
well but the usually the two excitations mix with same signs to produce
the dipole allowed state. In several cases the signs are opposite,
however. Inspecting the orbitals showed that in same sign cases the beta
LUMO is the mirror image of the alpha HOMO. In opposite sign cases alpha
HOMO and alpha LUMO start with the same sign of the coefficients. Thus,
if the relative signs of alpha and beta orbitals are random, it makes
sense that the signs are sometimes same and somtimes different. If they
are not, I have a problem to understand what is going on.

Does anyone know more about this? I do not think that this has to do
with the program I am using, but it is the much discussed G03.

Thanks in advance for comments,
Ulrike
--
Ulrike Salzner
Associate Professor
Department of Chemistry
Bilkent University
06800 Bilkent, Ankara
Turkeyhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt


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