Firefly and PC GAMESS-related discussion club

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Alex Granovsky
gran@classic.chem.msu.su

the short answer is that you cannot.
Any post-SCF calculations, including MP2, should run with at least
default settings; and in many cases you need to tighten them (e.g.,
in the case of partial linear dependence).

regards,
Alex Granovsky


On Tue Jan 5 '10 4:08am, alex wrote
-----------------------------------
>It works, thank you (it took some time to check, sorry for delay)!

>Dear Pedro, and anybody else who have experience in firefly code, would you be so kind to answer a question: is it true to say that small value of MP2 correction energies means (in the most cases) small error in gradients and thus validate poor convergence criteria at the input? If so I can calculate say 1000 of dimmers with light parameters NCONV=3 CUTOFF=1e-7 and save a lot of CPU time then recalculate only ~5-10 (<1%!!!!) with more demanding ones.

>Alex

>On Sat Jan 2 '10 4:01pm, Pedro Silva wrote
>------------------------------------------
>>Your input has:

>> $MP2 METHOD=1 DM2MET=-2 DIRECT=.T. CUTOFF=1.d-7 $END                        
>>                                                  
>> $SCF DIRSCF=.T. NCONV=3 DIIS=.T. SOSCF=.F. $END    

>>You should decrease you cutoff sharply (I suggest 1d-13), as well as the convergence criterion (I use NCONV=7). NCONV=3 gives you very poor gradients, and MP2 compuations need good gradient information.

>>Pedro