Sent to CCL by: Mariusz Radon [mariusz.radon~~gmail.com] Sue L chsue2004:yahoo.com wrote:
Is it necessary to put a keyword guess=mix, in order to locate a broken-symmetry singlet state in Gaussian? If the molecule contains a symmetry, in which the singly occupied alpha and beta orbitals are in different symmetry, there is no need to put that keyword?
Hi Sue,Is it enough or not, I think, it depends on particular case... You always need to check whether you really have converged to a broken-symmetry solution or not; AFAIK, even "guess=mix" keyword doesn't guarantee this. So, you need to inspect the molecular orbitals and/or <S**2> value after the calculations are finished.
In such a case, that alpha and beta singly occupied orbitals belong to different symmetries, a nice way to produce the broken symmetry solution might be to manually permute the relevant orbitals (e.g. "guess=alter") and (probably) to use "scf=symm".
best wishes, Mariusz Radon