From owner-chemistry _-at-_)ccl.net Thu Dec 13 11:29:01 2007 From: "Marcel Swart marcel.swart_._icrea.es" To: CCL Subject: CCL: origin of ab initio/basis set empiricism Message-Id: <-35841-071213095822-18483-rCtRnQMVaPkJxIugnlCAZQ()server.ccl.net> X-Original-From: Marcel Swart Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859-1; delsp=yes; format=flowed Date: Thu, 13 Dec 2007 15:58:04 +0100 Mime-Version: 1.0 (Apple Message framework v752.3) Sent to CCL by: Marcel Swart [marcel.swart-*-icrea.es] About the basis sets extrapolation, it is done, see for instance: Bak, J=F8rgensen, Olsen, Helgaker, Klopper J. Chem. Phys. 2000, 112, 9229-9242 On Dec 13, 2007, at 2:39 PM, Rene Fournier renef++yorku.ca wrote: > > Sent to CCL by: Rene Fournier [renef(a)yorku.ca] > Hello, > I agree on > >> All commonly used basis >> sets, even the Pople-style sets, are generated by optimizing >> exponents and contraction coefficients to minimize (ab initio) >> energies of atoms and sometimes molecules. > > That's correct. But there are other problems with choices of basis > sets and that's where empiricism can creep in. How many contracted > functions is enough? What's the best contraction pattern? > (why 6-31G and not 6-21G? or 4-31G? or 9-61G? or 7-1111G?) > How many polarization functions? Why not throw in a few bond-=20 > centered functions? > Many basis sets went into oblivion not because they gave higher =20 > energies > for atoms or molecules --- adding more functions and keeping them =20 > uncontracted > always lowers energy. It's that they did not give good agreement =20 > with experimental > bond lengths, bond energies etc. relative to other basis sets of =20 > comparable > computational cost. I'm not sure how to call methods where high-=20 > level theory > is used instead of experiment as the reference to assess goodness =20 > of a lower level > of theory (maybe a smaller basis). I think it's still empirical =20 > because there's > the assumption that if the low-level theory reproduces high-level =20 > theory to > within some accuracy for cases X, Y, Z, it will also reproduce high-=20= > level > level theory to that accuracy for other cases when we do applications. > ( There's also the obvious point that if the high-level theory =20 > reference is > really, really good, then it IS the experimental result! ) > It is possible to take empiricism out of basis set choice by doing > many calculations in a sequence with increasingly big basis sets =20 > defined > by only 1 and maybe 2 parameters, so that one can crank up accuracy =20= > smoothly, > and extrapolate results to "infinite basis set". Basis sets =20 > suitable for > that are: > - even-tempered fully uncontracted basis sets (K Ruedenberg); > - plane-waves (increase energy cut-off and box size); > - all-numerical programs (mostly for diatomics, Becke's NUMOL for =20 > polyatomics). > But I don't see that done very often, even with plane-waves where =20 > it would be > easy I suppose. > > Regards, > Rene > > Rene Fournier Office: 303 Petrie > Chemistry Dpt, York University Phone: (416) 736 2100 Ext. 30687 > 4700 Keele Street, Toronto FAX: (416)-736-5936 > Ontario, CANADA M3J 1P3 e-mail: renef---yorku.ca > > > > > On Wed, 12 Dec 2007, Kirk Peterson kipeters-*-wsu.edu wrote: > >> >> Sent to CCL by: Kirk Peterson [kipeters-$-wsu.edu] >> >> As a sidebar to this discussion, I have to strongly disagree that >> basis set parameters, exponents or contraction coefficients, >> use empirical data in their construction. All commonly used basis >> sets, even the Pople-style sets, are generated by optimizing >> exponents and contraction coefficients to minimize (ab initio) >> energies of atoms and sometimes molecules. Some of the Pople-style >> basis sets utilize scale factors to apply to atom-optimized =20 >> exponents, >> but these were based on (ab initio) molecular calculations >> and not experimental data. >> >> regards, >> >> -Kirk >> >> On Dec 12, 2007, at 8:21 AM, Rene Fournier renef+*+yorku.ca wrote: >> >>> >>> Sent to CCL by: Rene Fournier [renef\a/yorku.ca] >>> David Craig and Robert Parr first used "ab initio" in quantum >>> chemistry, >>> see >>> http://www.quantum-chemistry-history.com/Parr1.htm >>> Near the middle of that page, Parr recounts: >>> >>> " Craig and I published this paper on "configuration interaction in >>> benzene", where we took the pi-system and did essentially a complete >>> configuration interaction calculation on it. >>> >>> That has some trivial historical interest in that it was there that >>> the >>> word, the term ab initio was introduced. Craig and Ross had computed >>> everything from the start in London and I had personally computed >>> everything from start in Pittsburgh. Then we compared our answers >>> when we >>> were finished- This involved computing of all the integrals as =20 >>> best as >>> they could be done and selecting the configurations to mix for the >>> ground >>> and exited states because there were electronic states that were of >>> experimental interest and we checked our answers one against each >>> other >>> when we were finished. And what the paper says is, that these >>> calculations >>> were done ab initio by Craig and Ross and by me, independently. And >>> Mulliken later said that this was the introduction of the term ab >>> initio >>> into quantum chemistry. In the short review that you have, I talk >>> about >>> this and reproduce a picture of a letter from Craig to me where he >>> uses >>> the term ab initio in a different context. So ab initio was >>> introduced in >>> the quantum chemistry by Craig in a letter to me and I put it =20 >>> into the >>> manuscript. That's where ab initio came from. " >>> >>> >>> Funny thing is Parr later became a champion of Density Functional >>> Theory >>> and for many years (70's, 80's) DFT practitioners were often >>> criticized >>> for doing calculations that were not "ab initio". I think views =20 >>> have >>> changed now; "first-principles" was introduced probably to say >>> "mostly >>> not empirical" but without the implications "ab initio" had acquired >>> over >>> the years. The term "ab initio calculation", as it's commonly used, >>> very rarely refers to a calculation "devoid of empiricism", for >>> example >>> the choice of basis set parameters is almost always empirical, >>> see discussion on >>> http://www.ccl.net/chemistry/resources/messages/2001/11/28.002-=20 >>> dir/index.html >>> >>> Rene Fournier Office: 303 Petrie >>> Chemistry Dpt, York University Phone: (416) 736 2100 Ext. 30687 >>> 4700 Keele Street, Toronto FAX: (416)-736-5936 >>> Ontario, CANADA M3J 1P3 e-mail: renef*_*yorku.ca >>> >>> >>> On Wed, 12 Dec 2007, Christoph Etzlstorfer christoph.etzlstorfer . >>> jku.at wrote: >>> >>>> There is a story about that in Michael J.S. Dewars biography "A >>>> semiempirical life", American Chemical Society, 1992, p. 129. >>>> >>>> Best regards >>>> >>>> Christoph >>>> >>>> >>>> Am 11.12.2007 um 03:13 schrieb Tommy Ohyun Kwon ohyun.kwon _ >>>> chemistry.gatech.edu: >>>> >>>>> >>>>> Sent to CCL by: Tommy Ohyun Kwon [ohyun.kwon . =20 >>>>> chemistry.gatech.edu] >>>>> Dear CCLers; >>>>> I would appreciate it if anyone could tell me who used the term of >>>>> "ab initio >>>>> calculations" first. >>>>> Thank you very much for your kind attention. >>>>> >>>>> Best wishes, >>>>> >>>>> Tommy >>>>> >>>>> >>>>> -- >>>>> Tommy Ohyun Kwon, Ph.D >>>>> School of Chemistry and Biochemistry >>>>> Georgia Institute of Technology >>>>> Atlanta Georgia, 30332 >>>>> Email: ohyun.kwon]*[chemistry.gatech.edu >>>>> >>>>> >>>>> >>>>> -=3D This is automatically added to each message by the mailing >>>>> script =3D- >>>>> To recover the email address of the author of the message, please >>>>> change> Conferences: http://server.ccl.net/chemistry/=20 >>>>> announcements/ >>>>> conferences/ >>>>> >>>>> Search Messages: http://www.ccl.net/htdig (login: ccl, Password: >>>>> search)> >>>>> >>>> >>>> #################################################### >>>> www.etzlstorfer.com >>>> *********************************************************** >>>> Dr. Christoph Etzlstorfer Phone: *43-732-2468-8750 >>>> Universitaet Linz Fax: *43-732-2468-8747 >>>> A-4040 Linz E-mail: christoph.etzlstorfer,+,jku.at >>>> Austria http://www.orc.uni-linz.ac.at >>>> #################################################### >>>> >>>> >>>> >>>> >>>> >>> >>> >>> >>> -=3D This is automatically added to each message by the mailing = script >>> =3D- >>> To recover the email address of the author of the message, please >>> change> Conferences: http://server.ccl.net/chemistry/announcements/ >>> conferences/ >>> >>> Search Messages: http://www.ccl.net/htdig (login: ccl, Password: >>> search)> >> >> > > > > -=3D This is automatically added to each message by the mailing =20 > script =3D- > To recover the email address of the author of the message, please =20 > change> Conferences: http://server.ccl.net/chemistry/announcements/=20 > conferences/ > > Search Messages: http://www.ccl.net/htdig (login: ccl, Password: =20 > search)> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D dr. Marcel Swart ICREA researcher at Institut de Qu=EDmica Computacional Universitat de Girona Parc Cient=EDfic i Tecnol=F2gic Edifici Jaume Casademont (despatx A-27) Pic de Peguera 15 17003 Girona Catalunya (Spain) tel +34-972-183240 fax +34-972-183241 e-mail marcel.swart|-|icrea.es marcel.swart|-|udg.edu web http://www.icrea.es/pag.asp?id=3DMarcel.Swart http://iqc.udg.edu/~marcel =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D