From owner-chemistry@ccl.net Wed May 31 07:08:00 2006
From: "Marcin Makowski makowskm=-=chemia.uj.edu.pl" <owner-chemistry.:.server.ccl.net>
To: CCL
Subject: CCL: negative bsse content
Message-Id: <-31869-060531070632-22347-Y3QEVQEVoowf8wwUTYbDkQ.:.server.ccl.net>
X-Original-From: "Marcin Makowski" <makowskm+/-chemia.uj.edu.pl>
Date: Wed, 31 May 2006 07:06:28 -0400
Sent to CCL by: "Marcin Makowski" [makowskm-x-chemia.uj.edu.pl]
Very general thing is that actual LMP2 implementation is an approximation
to exact MP2 relying (by cut-offs introduced) on localization of orbitals.
In this method and in hte limit of perfect localization BSSE should just disappear. For this reason BSSE here has good chance to be quite small.
I wouldn't be suprised if subtle changes in the shape of localized
orbitals and effective partition of space between separate computations
could actually transform some small positive net effect into small negative.
The result is not physical, but I wouldn't worry too much about it if the values are under 1 kcal. If you want to
get some more confidence, try decreasing cut-off tresholds of the LMP2
method and see if you obtain smooth behaviour.
Yours,
Marcin
> Sent to CCL by: Jozsef Csontos [jozsefcsontos[a]creighton.edu]
> Dear List Members,
>
> I was calculating intermolecular interaction energies using the
> counterpoise method to correct the results for bsse (3 dimer centered
> basis set calcs). The bsse contents were also calculated (2 more monomer
> centered basis set calcs). If I'm not mistaken I can get the bsse
> content if I subtract the non-bsse corrected energy from the bsse
> corrected one. This imply that the bsse content should be positive.
>
> I am using quite large basis set considering the investigated systems
> (~50 atoms, cc-pVTZ, aug-cc-pVTZ) and the BSSE content is usually small,
> less than 1kcal/mol; the interaction energies are in the 2-8 kcal/mol
> range. The level of theory are lmp2 and dft.
>
> However, in some cases (mainly lmp2 calcs) I got small negative (~
> -0.3,-0.5 kcal/mol) bsse contents.
>
> Do you have any idea, how the bsse content can come to be negative?
>
> Thanks,
> Jozsef
>
>
> --
> Jozsef Csontos, Ph.D.
>
> Department of Biomedical Sciences
> Creighton University,
> Omaha, NE
From owner-chemistry@ccl.net Wed May 31 07:49:01 2006
From: "Tanja van Mourik tanja.vanmourik%x%st-andrews.ac.uk" <owner-chemistry-x-server.ccl.net>
To: CCL
Subject: CCL: negative bsse content
Message-Id: <-31870-060531064727-21144-Y+dZXlzaw/ecsJLLHJWbQQ-x-server.ccl.net>
X-Original-From: Tanja van Mourik <tanja.vanmourik---st-andrews.ac.uk>
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Date: Wed, 31 May 2006 11:11:22 +0100
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Sent to CCL by: Tanja van Mourik [tanja.vanmourik^-^st-andrews.ac.uk]
Dear Joszef,
>
> I was calculating intermolecular interaction energies using the
> counterpoise method to correct the results for bsse (3 dimer centered
> basis set calcs). The bsse contents were also calculated (2 more monomer
> centered basis set calcs). If I'm not mistaken I can get the bsse
> content if I subtract the non-bsse corrected energy from the bsse
> corrected one. This imply that the bsse content should be positive.
>
> I am using quite large basis set considering the investigated systems
> (~50 atoms, cc-pVTZ, aug-cc-pVTZ) and the BSSE content is usually small,
> less than 1kcal/mol; the interaction energies are in the 2-8 kcal/mol
> range. The level of theory are lmp2 and dft.
>
> However, in some cases (mainly lmp2 calcs) I got small negative (~
> -0.3,-0.5 kcal/mol) bsse contents.
>
> Do you have any idea, how the bsse content can come to be negative?
BSSE is a negative quantity: it is calculated as the difference between
the sum of the monomer energies calculated in the dimer basis set and
the sum of the monomer energies calculated in the monomer basis set, all
of these at the geometries they adopt in the complex. It can also be
calculated by subtracting the CP-corrected interaction energy from the
uncorrected interaction energy (i.e., other way around compared to what
you say above), but -only- when the deformation energies are included in
the CP-corrected interaction energy. Perhaps some formulas can help
(with latex-style sub- and superscripts):
BSSE = E_{A}^{AB}(AB) + E_{B}^{AB}(AB) - E_{A}^{A}(AB) - E_{B}^{B}(AB)
where the subscripts, _{A} and _{B}, denote the molecular systems; the
superscipts, ^{A}, ^{B} and ^{AB}, denote the basis set (monomer or
dimer centred basis sets), and the (AB) in round brackets denotes that
all these are calculated at the optimised geometry of the dimer AB.
Using the same notation:
DeltaE(CP) = E_{AB}^{AB}(AB) - E_{A}^{AB}(AB) - E_{B}^{AB}(AB) +
E_{A}^{A}(AB) + E_{B}^{B}(AB) - E_{A}^{A}(A) - E_{B}^{B}(B)
DeltaE(noCP) = E_{AB}^{AB}(AB) - E_{A}^{A}(A) - E_{B}^{B}(B)
where E_{A}^{A}(A) is the energy of A at the equilibrium geometry of A,
(A), calculated in the monomer basis set.
The deformation energy of monomer A is:
Edef_{A} = E_{A}^{A}(AB) - E_{A}^{A}(A)
Comparing DeltaE(CP) and Delta(noCP) you can see that the difference
between these two equation is just the definition of the BSSE:
DeltaE(CP) = DeltaE(noCP) - BSSE
It sounds to me that you are calculating the BSSE as:
BSSE = E_{A}^{AB}(AB) + E_{B}^{AB}(AB) - E_{A}^{A}(A) - E_{B}^{B}(B)
(or with opposite sign), in which case you may get positive as well as
negative results (depending on how large the monomer deformation
energies are). The difference between this wrong definition of BSSE and
the correct BSSE is the sum of the monomer deformation energies.
For the formulas, see also:
Adv. Quant. Chem. 31, pp 105-135 (1999)
or less elaborately in some of my other papers, for example:
Phys. Chem. Chem. Phys. 5, pp 4519-4526 (2003)
Hope this helps,
Tanja
--
=================================================================
Tanja van Mourik
Royal Society University Research Fellow
School of Chemistry, University of St. Andrews
North Haugh, St. Andrews
Fife KY16 9ST, Scotland (UK)
email: tanja.vanmourik-#-st-andrews.ac.uk
web: http://chemistry.st-and.ac.uk/staffmember.php?id=tvm
=================================================================
From owner-chemistry@ccl.net Wed May 31 11:00:00 2006
From: "Jan Labanowski janl(-)speakeasy.net" <owner-chemistry-x-server.ccl.net>
To: CCL
Subject: CCL: CCL Moderator reminders and appeals
Message-Id: <-31871-060531105448-31908-qBz0ys9oMKOkHPBYessrUg-x-server.ccl.net>
X-Original-From: "Jan Labanowski" <janl=-=speakeasy.net>
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Date: Wed, 31 May 2006 14:54:39 +0000
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Sent to CCL by: "Jan Labanowski" [janl*speakeasy.net]
Dear CCL Members,
The vacations time is approaching, so few reminders:
0) When you send a message to CCL remember that it will be posted
ONLY after you confirm it (you will get a confirmation request
by e-mail -- if it does not show up, check your spambox!).
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If you are a group member, tell your boss about the Job Service at:
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those who look for a job and you will be doing them a favor.
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support is very WELCOME!). Go to:
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Submit interesting conferences/workshop/symposium there even
if you are not associated with the conference.
3) If you are leaving for prolonged vacations and your mailbox
quota is small, please consider unsubscribing from CCL at:
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You can always resubscribe when you return, and you can
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4) Please upload materials to CCL Archives
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Consider "Adopting a CCL Page" by your company or your group.
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grep/find/awk/perl/whatever the files on the DVD on your local
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7) CCL.NET is an old and recognized domain. It is indexed by all major
search engines. Tell me how CCL can help you in promoting your
web site, software, consulting, etc. You will capitalize
on the CCL established status on the Internet and support CCL
at the same time. I will help you if you help CCL.
Note... There are so many companies that service Computational
Chemistry, Cheminformatics, Bioinformatics, etc., and so on...
Ask them to support CCL! You may have learned about them by
looking at list of CCL Links:
http://server.ccl.net/chemistry/links/index.shtml
yet, they do not support CCL beside the
http://nanoandgiga.com and the http://sunsetmolecular.com/
that "Adopted the CCL Page" and the ones listed on Supporters Page at:
http://server.ccl.net/cgi-bin/ccl/supporting_members
Thank you for your attention...
Your CCL Moderator
Jan Labanowski, Ph.D.
jkl : ccl.net
From owner-chemistry@ccl.net Wed May 31 11:34:01 2006
From: "manuel alonso tarajano%x%bioinfo.cu" <owner-chemistry++server.ccl.net>
To: CCL
Subject: CCL: problems with charged residues at MDyn
Message-Id: <-31872-060531103810-27707-g9sKEnK9uqFRADQRa4d2bg++server.ccl.net>
X-Original-From: manuel alonso <tarajano*bioinfo.cu>
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Date: Wed, 31 May 2006 09:42:22 -0400
MIME-Version: 1.0
Sent to CCL by: manuel alonso [tarajano%%bioinfo.cu]
hello list:
(first of all .. im very new at charmm .. so i hope you will apologize
any tribial question)
i know you have had a lot of disscusions here about protonation states
of a.acids residues ..but till now
I havent found the one that could help me
Im running (trying to) a MDyn to a small peptide with titratable groups
and I think CHARMM
is complaining about its protonations state and cos of this my MDyns
runs are dying.
Here I post part of the output I think is more related to the problem :
.
.
.
. (here are my titratable residues)
.
***** Message from SEQRDR ***** THE SYSTEM CONTAINS 9 TITRATABLE GROUPS
THE USER MUST PREDETERMINE THE PROTONATION STATE THROUGH THE SEQUENCE
AND RTF
HIS - 0 ASP - 3 GLU - 2 LYS - 4 TYR - 0
.
.
.
. (here are the warnings)
.
.
.
TITLE> *
** WARNING ** For atom in coordinate file, the residue type does not
match that (RESN) in the PSF: 2 PSF= THR INPUT= ASN
** WARNING ** For atom in coordinate file, the residue type does not
match that (RESN) in the PSF: 2 PSF= THR INPUT= ASN
** WARNING ** For atom in coordinate file, the residue type does not
match that (RESN) in the PSF: 2 PSF= THR INPUT= ASN
** WARNING ** For atom in coordinate file, the residue type does not
match that (RESN) in the PSF: 2 PSF= THR INPUT= ASN
** WARNING ** For atom in coordinate file, the residue type does not
match that (RESN) in the PSF: 2 PSF= THR INPUT= ASN
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 6 IRES= 2 RESID=3 RES=ASN ATOM=CG
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 7 IRES= 2 RESID=3 RES=ASN ATOM=OD1
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 8 IRES= 2 RESID=3 RES=ASN ATOM=ND2
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 14 IRES= 3 RESID=4 RES=THR ATOM=OG1
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 15 IRES= 3 RESID=4 RES=THR ATOM=CG2
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 22 IRES= 4 RESID=5 RES=ASP ATOM=OD1
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 23 IRES= 4 RESID=5 RES=ASP ATOM=OD2
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 40 IRES= 6 RESID=7 RES=GLN ATOM=OE1
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 41 IRES= 6 RESID=7 RES=GLN ATOM=NE2
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 47 IRES= 7 RESID=8 RES=LYS ATOM=CG
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 48 IRES= 7 RESID=8 RES=LYS ATOM=CD
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 49 IRES= 7 RESID=8 RES=LYS ATOM=CE
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 50 IRES= 7 RESID=8 RES=LYS ATOM=NZ
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 56 IRES= 8 RESID=9 RES=VAL ATOM=CG1
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 57 IRES= 8 RESID=9 RES=VAL ATOM=CG2
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 63 IRES= 9 RESID=10 RES=SER ATOM=OG
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 69 IRES= 10 RESID=11 RES=GLU ATOM=CG
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 71 IRES= 10 RESID=11 RES=GLU ATOM=OE1
** WARNING ** For atom in coordinate file, the corresponding residue in
the PSF lacks that atom:
INDEX= 72 IRES= 10 RESID=11 RES=GLU ATOM=OE2
** WARNING ** For atom in coordinate file, could not find residue in
PSF, and is thus ignored:
SEGID= RESID=32 RESNAME= MET TYPE= N
*** LEVEL 1 WARNING *** BOMLEV IS 0
** WARNING ** For atom in coordinate file, could not find residue in
PSF, and is thus ignored:
SEGID= RESID=32 RESNAME= MET TYPE= CA
*** LEVEL 1 WARNING *** BOMLEV IS 0
** WARNING ** For atom in coordinate file, could not find residue in
PSF, and is thus ignored:
SEGID= RESID=32 RESNAME= MET TYPE= C
*** LEVEL 1 WARNING *** BOMLEV IS 0
** WARNING ** For atom in coordinate file, could not find residue in
PSF, and is thus ignored:
SEGID= RESID=32 RESNAME= MET TYPE= O
*** LEVEL 1 WARNING *** BOMLEV IS 0
** WARNING ** After reading, there are no coordinates for selected
atom: 1 1 ASN HT1
** WARNING ** After reading, there are no coordinates for selected
atom: 2 1 ASN HT2
** WARNING ** After reading, there are no coordinates for selected
atom: 3 1 ASN N
** WARNING ** After reading, there are no coordinates for selected
atom: 4 1 ASN HT3
** WARNING ** After reading, there are no coordinates for selected
atom: 5 1 ASN CA
** WARNING ** After reading, there are no coordinates for selected
atom: 6 1 ASN CB
** WARNING ** After reading, there are no coordinates for selected
atom: 7 1 ASN CG
** WARNING ** After reading, there are no coordinates for selected
atom: 8 1 ASN OD1
** WARNING ** After reading, there are no coordinates for selected
atom: 9 1 ASN ND2
** WARNING ** After reading, there are no coordinates for selected
atom: 10 1 ASN HD21
** A total of 133 selected atoms have no coordinates
** A total of 64 warnings were encountered during coordinate reading **
** MESSAGE ** 8 atoms in coordinate file were outside the specified
sequence range.
*** LEVEL 2 WARNING *** BOMLEV IS 0
** WARNING ** 204 atoms in coordinates file had a sequence mismatch.
*** LEVEL 0 WARNING *** BOMLEV IS 0
BOMLEV HAS BEEN SATISFIED. TERMINATING.
Im currently using CHARMM 30b1
I guess im missing to supply CHARMM with some PSF file/data related to
titratable groups, but I dont know which file might this be or if I
should provide CHARMM with some info to handle titratable groups at a
given pH.
I think I remeber that for example histidine (HIS) has two different
3-letters-code for its two protonations states ,
maybe i must provide charmm with the rights 3-letters-codes for my
titrable groups ? if so.. where could i find those codes ?
thanks to all in advance
and please let me know if you need some more data in order to help me
tarajano
(the initial part of my input file is:)
**********************************************************
**********************************************************
open unit 1 card read name toph19_eef1.inp
read RTF card unit 1
close unit 1
open unit 1 card read name param19_eef1.inp
read PARA card unit 1
close unit 1
open unit 1 card read name "xxxxxx.pdb"
read sequ pdb unit 1
generate prot setu
! pdb
open unit 1 card read name "xxxxxx.pdb"
read coor pdb unit 1
close unit 1
! hydrogens
hbuild sele all end
! build
ic fill
ic para
ic build
open unit 1 card write name "xxxxxx.pdb"
write coor pdb unit 1
close unit 1
**********************************************************
**********************************************************
From owner-chemistry@ccl.net Wed May 31 12:56:00 2006
From: "Rick Venable rvenable.:.pollux.cber.nih.gov" <owner-chemistry~!~server.ccl.net>
To: CCL
Subject: CCL: problems with charged residues at MDyn
Message-Id: <-31873-060531125347-30107-cyRsZ4MLWnOqsFuH6qNW9w~!~server.ccl.net>
X-Original-From: Rick Venable <rvenable^pollux.cber.nih.gov>
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Date: Wed, 31 May 2006 12:49:45 -0400
MIME-Version: 1.0
Sent to CCL by: Rick Venable [rvenable/a\pollux.cber.nih.gov]
The CHARMM forums at URL www.charmm.org may be a better choice
for this sort of question, and the web site does support the use of
attachments (CCL does not, for understandanle email security reasons).
The 'titratable group' message is warning only, a reminder to
carefully review choices made about things such as the location and
number of protons on the HIS ring. There are likely other errors.
On Wed, 31 May 2006, manuel alonso tarajano%x%bioinfo.cu wrote:
> (first of all .. im very new at charmm .. so i hope you will apologize
> any tribial question) i know you have had a lot of disscusions here
> about protonation states of a.acids residues ..but till now I havent
> found the one that could help me Im running (trying to) a MDyn to a
> small peptide with titratable groups and I think CHARMM is complaining
> about its protonations state and cos of this my MDyns runs are dying.
> Here I post part of the output I think is more related to the problem
-------------------------------------
Rick Venable 29/500
Membrane Biophysics Section
NIH/NHLBI Lab. of Comp. Biology
Bethesda, MD 20892-8014 U.S.A.
(301) 496-1905 Rick_Venable AT nih*gov
ALT email: rvenable AT speakeasy*org
-------------------------------------
From owner-chemistry@ccl.net Wed May 31 13:32:01 2006
From: "Eric Hu list.eric^gmail.com" <owner-chemistry^_^server.ccl.net>
To: CCL
Subject: CCL: freeze internal coordinates in G03
Message-Id: <-31874-060531132933-22940-rFdwrv37CCmUMecNbYd9AQ^_^server.ccl.net>
X-Original-From: "Eric Hu" <list.eric*|*gmail.com>
Content-Type: multipart/alternative;
boundary="----=_Part_15212_9871662.1149096565091"
Date: Wed, 31 May 2006 10:29:25 -0700
MIME-Version: 1.0
Sent to CCL by: "Eric Hu" [list.eric]|[gmail.com]
------=_Part_15212_9871662.1149096565091
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Hi, I want to freeze two monomers in a dimer structure during a geometry
optimization. ModRedundant provides several ways to freeze bond length,
angle and dihedral angles. Since I want to freeze any internal geometry
optimization within the monomer and am only interested in their relative
orientation in the dimer, I wonder if there are more concise ways to deal
with this besides using B ** F, A***F and D***F for every atom. Thanks.
Eric
------=_Part_15212_9871662.1149096565091
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
<div>Hi, I want to freeze two monomers in a dimer structure during a
geometry optimization. ModRedundant provides several ways to freeze
bond length, angle and dihedral angles. Since I want to freeze any
internal geometry optimization within the monomer and am only
interested in their relative orientation in the dimer, I wonder if
there are more concise ways to deal with this besides using B ** F,
A***F and D***F for every atom. Thanks.<br></div>
<span>
<br>
Eric</span>
------=_Part_15212_9871662.1149096565091--
From owner-chemistry@ccl.net Wed May 31 14:58:00 2006
From: "Jozsef Csontos jozsefcsontos|a|creighton.edu" <owner-chemistry{:}server.ccl.net>
To: CCL
Subject: CCL: negative bsse content
Message-Id: <-31875-060531145149-23464-wVyHGiFQEfUrpTWJ8TpocA{:}server.ccl.net>
X-Original-From: Jozsef Csontos <jozsefcsontos-x-creighton.edu>
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Date: Wed, 31 May 2006 13:51:39 -0500
Mime-Version: 1.0
Sent to CCL by: Jozsef Csontos [jozsefcsontos%%creighton.edu]
Hi Tanja,
> Dear Joszef,
>
> BSSE is a negative quantity: it is calculated as the difference between
> the sum of the monomer energies calculated in the dimer basis set and
> the sum of the monomer energies calculated in the monomer basis set, all
> of these at the geometries they adopt in the complex.
> Perhaps some formulas can help
> (with latex-style sub- and superscripts):
>
> BSSE = E_{A}^{AB}(AB) + E_{B}^{AB}(AB) - E_{A}^{A}(AB) - E_{B}^{B}(AB)
you are right, equations can help, sorry for neglecting them.
I calculated the interaction energy according to the original
Boys-Bernardi procedure:
DeltaE(CP)=E_{AB}^{AB}(AB) - E_{A}^{AB}(AB) - E_{B}^{AB}(AB)
in this case the non corrected interaction energy is
DeltaE(noCP) = E_{AB}^{AB}(AB) - E_{A}^{A}(A) - E_{B}^{B}(B)
The difference between the two is the bsse content, which is the same as
you stated above.
Some words about the sign, I think the sign of the bsse is the matter of
definition:
(+) JCC, 25, 1771, 2004
(-) JCC, 22, 196, 2001
I used the DeltaE(CP)-DeltaE(noCP) equation which implies that the bsse
is positive. This gave me results with opposite sign comparing to yours:
> DeltaE(CP) = DeltaE(noCP) - BSSE
>
As you might noticed, I didn't correct for deformation (fragment
relaxation), but it vanishes anyway when you subtract the interaction
energies.
So, apart from the signs, I should always get results on the same side
of zero, but I didn't.
Best wishes,
Jozsef
PS.: I tend to accept Marcin's opinion.
>I wouldn't be suprised if subtle changes in the shape of localized
>orbitals and effective partition of space between separate computations
>could actually transform some small positive net effect into small
>negative.
--
Jozsef Csontos, Ph.D.
Department of Biomedical Sciences
Creighton University,
Omaha, NE
From owner-chemistry@ccl.net Wed May 31 17:25:00 2006
From: "Serguei Patchkovskii ps.:.ned.sims.nrc.ca" <owner-chemistry . server.ccl.net>
To: CCL
Subject: CCL: negative bsse content
Message-Id: <-31876-060531172244-31239-H4GfxyatwKBbp35/necG+g . server.ccl.net>
X-Original-From: Serguei Patchkovskii <ps*_*ned.sims.nrc.ca>
Content-Type: TEXT/PLAIN; charset=US-ASCII
Date: Wed, 31 May 2006 16:41:53 -0400 (EDT)
MIME-Version: 1.0
Sent to CCL by: Serguei Patchkovskii [ps,ned.sims.nrc.ca]
On Wed, 31 May 2006, Jozsef Csontos jozsefcsontos|a|creighton.edu wrote:
> BSSE = E_{A}^{AB}(AB) + E_{B}^{AB}(AB) - E_{A}^{A}(AB) - E_{B}^{B}(AB)
[...]
> So, apart from the signs, I should always get results on the same side
> of zero, but I didn't.
Given the above definition, you can expect BSSE to be non-positive as long
as the method used to calculate the energies is variational. The argument
goes as follows: A bigger variational space (A in the combined A+B basis set)
can only lead to lower energies compared a smaller variational space (A in
the A basis set alone). Therefore, the difference E_{A}^{AB}(AB)-E_{A}^{A}(AB)
must be negative (or zero). Same holds for the energy of B - so the sum of
the two quantities must be non-positive as well.
This argument breaks down if:
a) the method you are using is not variational
or
b) the basis set alone does not represent the entire variational space of
the method
or
c) there is numerical noise in the calculations, which exceeds the magnitude
of the BSSE
Because MP2 energy is not variational, there is no reason to expect a
definite sign of BSSE for MP2 (either canonical or localized).
In the case of DFT, there is both a "hidden" variational space (numerical
integration grid) and a possibility of having significant numerical noise.
Both effects should decrease with the use of better grids.
Serguei