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Alex Granovsky
gran@classic.chem.msu.su

mix=.t. works for both HF and DFT but there is no warranty that
you will indeed obtain a broken-symmetry solution. You can try
several times using different settings for SCF convergers.

Alternatively, you can try to use better guess for broken-symmetry
solutions using e.g. AOMIX program by S. Gorelsky.

Note, with mix=.t. you need to switch symmetry off if HOMO and
LUMO are of different symmetry.

Kind regards,
Alex Granovsky



On Sat Dec 21 '13 7:42am, Pavlo Solntsev wrote
----------------------------------------------
>Dear FF users.

>Could you share your experience with broken-symmetry calculation using HF and DFT? I have an example below. If i use DFT i have Sz=0, S^2 = 0 for broken-symmetry singlet. If i use HF i have Sz=0 S^2 = 1.8. Which is reasonable. Does it mean, mix=.t. works only for HF? I know, we can remove switch symmetry completely off (nosym=1), and in this case i got S^2 = 0.8 for DFT which is also acceptable. I confused why we can use full orbital symmetry within HF, but not for DFT.

>Pavel.
>
>
> $SYSTEM MWORDS=50 $END
> $CONTRL RUNTYP=energy dfttyp=bp86  $END
> $CONTRL SCFTYP=UHF $END
> $CONTRL MAXIT=100 $END
> $CONTRL ICHARG=-2  MULT=1 $END
> $BASIS GBASIS=n31 ngauss=6  $END
> $BASIS ndfunc=1 $END
> $guess mix=.t. $end
> $DATA
>[Cu2F6]^-2 BS singlet
>Dnh 2

> CU         29.0   1.5298305586   0.0000000000   0.0000000000
> F           9.0   2.7561841734   1.3744839332   0.0000000000
> O           8.0   0.0000000000   1.1934572146   0.0000000000
> H           1.0   0.0000000000   2.1349088145   0.0000000000
> $end