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Re^2: About NSTATE, WSTATE and AVECOE in XMCQDPT2

Panwang Zhou
pwzhou@gmail.com


Dear Alex,

Thanks for you comments.

Best Regards,
Panwang Zhou


On Tue Oct 23 '12 8:48pm, Alex Granovsky wrote
----------------------------------------------
>Dear Panwang Zhou,

>Sorry for some delay with my response.

>Please see my comments below.
>
>
>On Mon Oct 22 '12 7:55am, Panwang Zhou wrote
>--------------------------------------------
>>Dear Alex,

>>I want to calculate vertical excitation energy between the ground state and the first excited state with XMCQDPT2, first I do a state-averaged MCSCF on the optimized S0 geometries, with the following settings:

>>$MCSCF CISTEP=ALDET FULLNR=.F. SOSCF=.T. MAXIT=100 $END
>>$DET NCORE=72 NACT=12 NELS=12 NSTATE=6 WSTATE(1)=1,1 $END

>>From this discussion club and the GAMESS-US manual I understand why the NSTATE should be larger than 2 as determinants do not correspond to any spin number and the triplet will also be obtained when the CISTEP=ALDET. The WSTATE(1)=1,1 will exclude the triplet and only do averaging on the first and second singlet.
>
>
>That's correct. In addition, Firefly v. 8.0.0 includes
>the possibility to filter triplets out but it's a different story

>>Then I using the optimized MCSCF MOs to do the XMCQDPT2 calculation with the following settings:

>>$MCSCF CISTEP=ALDET FULLNR=.F. SOSCF=.T. MAXIT=100 $END
>>$DET NCORE=72 NACT=12 NELS=12 NSTATE=6 WSTATE(1)=1,1 $END
>>$XMCQDPT NSTATE=10 EDSHFT=0.02 THRGEN=1D-12 INORB=2 $END
>>$XMCQDPT WSTATE(1)=1,1,-0 AVECOE(1)=1,1,-0 $END

>>Is this correct for calculating the vertical excitation energy between S0 and S1?

>It is correct provided you put the converged MOs into the $vec group
>of the input file and moread it using

>

 $guess
  guess=moread norb=the_total_number_of_MOS
 $end

>In addition, for better precision I'd suggest to use
>

 $contrl wide=.t. $end

>This will punch MOs with all significant digits.

>Alternatively, you can set inorb to zero and perform MCSCF then
>XMCQDPT2 computations using single input file.
>
>
>>I set NSTATE=10 because sanya has said "The size of the effective
>Hamiltonian given by NSTATE has serious effect on the transition
>energy (the energy grows with NSTATE and levels off at NSTATE~10)."

>That's not always true i.e. quite often nstate=2 is enough.
>However, unlike with other MS-MR-PT2 theories, with XMCQDPT2
>you do can improve results increasing NSTATE.
>
>
>>However, I'm not clear the relation between the NSTATE, WSTATE
>> and AVECOE in XMCQDPT2, could you comment on this? In the firefly
>> manual I could not find the explain for WSTATE in XMCQDPT.

>Both WSTATE and AVECOE arrays are used to define the state's weights
>used compute state-averaged density matrices. Technically, the
>averaging used to define semi-canonical orbitals and to define
>orbital energies of these orbitals, can be different. If both WSTATE
>and AVECOE are given, the first one defines the averaging used to
>compute orbitals while the second is used for energies. If only one
>of them is given in input, then the second one will be set to that
>provided in the input so that WSTATE and AVECOE will be identical.
>The latter option should be used almost exclusively unless one has
>really good reasons why to use different averaging for different
>stages.  
>
>
>Normally, for S0->S1 transitions one needs to average over S0 and S1
>only and with equal weights i.e. to set WSTATE(1)=1,1,-0

>>Additional two small questions:
>>From this dicussion club I know there are two ways to avoid CASCI integral transformation step in XMCQDPT calculation.
>>(1) First do the MCSCF calculation with the following settings:
>>$mcscf iforb=.t. sd=.t. $end
>>$contrl wide=.t. $end

>>The do the XMCQDPT with:
>>$guess guess=moread norb=the_overall_number_of_mos $end
>>$xmcqdpt inorb=2 iforb=0 $end

>>My question is: when the iforb is true in $mcscf, can the obained MOs be used for next MCSCF calculation, where the geometry is close to the previous one.

>Yes they can be used. They correspond exactly to the same overall
>wavefunction but with different MOs and CI vector components.

>>(2) Do the XMCQDPT wih the following settings:
>>$mcscf iforb=.t. $end
>>$xmcqdpt iforb(1)=-1,1,1 $end

>>My question is:  what is the value should be set for inorb in this
>condition?

>The only valid is the default i.e. inorb=0

>>
>>
>>Best Regards,
>>Panwang Zhou

>>

>Kind regards,
>Alex Granovsky

>


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