Subject: problems with the SCF convergence in Gaussian 03

From: Konstantin Kudin <konstantin_kudin = = = yahoo.com>
Date: Mon, 21 Mar 2005 09:17:40 -0800 (PST)

Hi all,

 This message is for those still suffering from the SCF convergence
problems in G03.

 The problems can happen when the system has lots of close in energy
electronic states.

 If the method is Hartree-Fock, or some hybrid functional (i.e.,
B3LYP), try the following options:

scf=(noincfock,conver=11,maxcyc=1025) iop(5/22=20)

 These options force the use of pure EDIIS which is more expensive but
has a better chance of converging to a low state. The cranked up
accuracy is needed to make the SCF run for a good number of cycles
which improves the chances to end up in a low state.

 With pure functionals (non-hybrid such as BLYP) one can end up with
fractional occupation numbers, so the skill required to converge
somewhere is higher (level shift is definitely needed). If there is
some interest in this, I can follow up with another message.

 Kostya

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