# CCL: Polarization Basis Functions

*From*: Jussi Lehtola <jussi.lehtola||helsinki.fi>
*Subject*: CCL: Polarization Basis Functions
*Date*: Fri, 31 Aug 2012 23:11:17 +0300

Sent to CCL by: Jussi Lehtola [jussi.lehtola:+:helsinki.fi]
On Fri, 31 Aug 2012 14:47:31 -0400
"Gustavo L.C. Moura gustavo.moura*ufpe.br"
<owner-chemistry^^^ccl.net>
wrote:
> Sent to CCL by: "Gustavo L.C. Moura" [gustavo.moura~!~ufpe.br]
> Dear CCL Readers,
> How are the exponents of the polarization functions
> determined in a basis set? Taking carbon as an example, I know that
> we may determine the exponents of the s and p basis functions through
> the minimization of the electronic energy of an atomic calculation.
> But, how to determine the exponents of the d, or even f, basis
> functions if they do not contribute to the energy of the isolated
> atom? I apologize if this question sounds too basic, but I failed to
> find an answer to this question in the internet or in my books. Thank
> you very much in advance for helping me with this question. Sincerely
> yours, Gustavo L.C. Moura
To determine polarization functions you need to use some other model
system than the atom in order to perform the energy optimization.
Optimal polarization functions depend somewhat on the chemical
environment, so many different molecules are often studied and then
the exponents averaged somehow to form the production basis set. See
e.g. Jensen's papers [JCP 115, 9113 (2001)].
On the other hand, correlation functions (which are often also called
polarization functions) can be determined from atomic calculations,
e.g. Dunning's work [JCP 90, 1007 (1989)].
It's also possible to forget all about energy optimization and tune
basis sets directly for particular properties using
completeness-optimization [JCC 27, 434 (2006)]. In fact, I have a
paper coming out soon on automatical basis set formation [JCP 137, ???
(2012), doi: 10.1063/1.4749272].
--
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Mr. Jussi Lehtola, M. Sc. Doctoral Student
jussi.lehtola^^^helsinki.fi Department of Physics
http://www.helsinki.fi/~jzlehtol University of Helsinki
Office phone: +358 9 191 50 632 Finland
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Jussi Lehtola, FM Tohtorikoulutettava
jussi.lehtola^^^helsinki.fi Fysiikan laitos
http://www.helsinki.fi/~jzlehtol Helsingin Yliopisto
TyÃpuhelin: (0)9 191 50 632
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