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Re^2: Speeding up ALTTRF during XMCQDPT2 calculations

Alex Granovsky

Dear Thom,

>Finally, with Firefly v. 8.0.0 it is possible to get rid of the
>first MQCACI and integral transformation procedures for some types
>of XMCQDPT2 jobs. These types are, however, the most typically
>used ones. I'll document this in my next post to this thread.

Assume the averaging is exactly the same in both SA-CASSCF and
XMCQDPT2 procedures i.e. the weights defined by the WSTATE arrays
are the exactly the same and refer to the same states. Provided
this is indeed the case, one can avoid the first integral transformation
and CASCI procedure (performed by the routine MQCACI) by overlapping
part of calculations with those performed at the MCSCF stage and
reusing them at XMCQDPT2 stage.

To use this feature, one needs to direct MCSCF code to form
semi-canonical Fock orbitals and to save core and active Fock
operators. This can be done as follows:

 $mcscf iforb=.t. $end

One also needs to instruct QDPT code to reuse this information:

 $xmcqdpt iforb(1)=-1,1,1 $end

This will do the trick.  

Kind regards,

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