MEMCHK ERROR durring third order response calculation

[rlt92]

I'm trying to do an MCSCF calculation using Dalton 2018.1 to compute 2nd order hyperpolarizabilities of nitrobenzene but when I run that calculation I'm running into a MEMCHK error that seams to occur during the response calculation phase. I've tried running dalton with different amounts of memory (default, 12G, and 16G) but the error still occurs.

Attached is the shell output and the dalton output file. Any advice on how to fix this issue?

[hjaaj]

There seems to be a memory allocation error when running with CSFs for cubic response. I think it will work if you run with determinants, to do that add the following to your input:

Code: Select all

*OPTIMIZATION
.DETERMINANTS
*CI VECTOR
.PLUS COMBINATIONS

-- Hans Jørgen.

PS. Your active space is not balanced, as can be seen from e.g. natural orbital occupancy close to 2. I usually use MP2 natural orbital occupancies to guide the selection of active space.

[rlt92]

Thanks for the reply!I'll let you know how it goes after I get a chance to run the calculation.

I have one additional question about choosing balanced active spaces. I was under the impression that a balanced active space would have an equal number of occupied vs unoccupied orbitals. Why is this incorrect and are there situations where an unbalanced orbital occupation would be more correct? I would also appreciate any recommending reading related to this question.

[hjaaj]

An unbalanced active space will never be more correct when doing response calculations. In fact, you have 10 electrons in 9 orbitals, so there will always at least be one occupied orbital without a correlating orbital ...

Another issue for balanced space, when the molecule has symmetry the primary correlating orbital is not always in the same irrep as the occupied orbital. (Textbook example: for homonuclear diatomics pi_u is bonding while the correlating antibonding orbital has pi_g symmetry.) In your case the two last irreps are pi orbitals, and clearly an orbital in symmetry 3 is correlating one of the orbitals in symmetry 4.

An MP2 natural orbital analysis shows that you probably want "3 3" orbitals in the last two irreps instead of "2 2".
You can get an MP2 natural orbital analysis by replacing .MCSCF with

Code: Select all

.HF
.MP2

and you can start the MCSCF from MP2 orbitals, a much better start guess than Huckel orbitals, with:

Code: Select all

.HF
.MP2
.MCSCF