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Re^2: Problem with SOC (spin-orbit coupling) calculations

Maksim Shundalau

Dear Alex!

Firstly I calculated terms of the YbCs molecule at the SA-CASSCF level of theory from asymptotical limit (20 A) to the shot distance (3 A) point-by-point with step 0.05 A. I get 3 valence electrons and 12 orbitals for active space, and 14 states (11 doublets and 3 quartets) in SA procedure. I use Stuttgart ECP basis sets. I perform single-point calculation at a certain point, and then I take optimized vectors from PUNCH and perform single-point calculation at a next point, etc. Also I’m watching the states in SA.
In result I have smooth PECs for the ground and some excited states of YbCs.
For example, for the ground state PEC I have:

7.65 A CAS=-52.5164130391
7.70 A CAS=-52.5163908210
7.75 A CAS=-52.5163695661
7.80 A CAS=-52.5163495738

Secondly I calculated the terms at the XMCQDPT2 level of theory, and again I have smooth PECs. The details of the XMCQDPT2 calculations I can also describe, but the SOC calculations are performed on the CAS-vectors.

At least I calculated SOC with optimized CAS-vectors, and I have a problem. I get “breaks” in PECs, for example:

7.65 A CAS+SOC=-52.5164465294
7.70 A CAS+SOC=-52.5164233281
deltaE=0.00000115 !!!!!!!!!!!!!!!!!!
7.75 A CAS+SOC=-52.5164221806
7.80 A CAS+SOC=-52.5163986729

Thank you very much,
With best regards,
Maksim Shundalau.

On Thu Jan 14 '16 4:16pm, Alex Granovsky wrote
>Dear Maksim,

>could you please describe in details your computational protocol?

>Kind regards,
>Alex Granovsky
>On Tue Jan 12 '16 12:16pm, Maksim Shundalau wrote
>>Dear Alex!

>>I’ m trying to calculate PECs of the YbCs molecule at the CAS(3,12)/XMCQDPT2 + SOC (spin-orbit coupling) level of theory with Stuttgart ECP basis sets.
>>I have smooth terms at the CAS(3,12) and at the XMCQDPT2 levels of theory. But I have “breaks” in PECs, when I’m calculating SOC (see, for example, figs.pdf).

>>What’s the problem here?

>>Thank you very much,
>>With best regards,
>>Maksim Shundalau.

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