I would like to run DFMP2 calculations using MP2FIT auxiliary basis sets. Is that possible to do that using psi4? I can do that using Molpro via the following input file, and basically want to do the same using psi4.
C -1.888896 -0.179692 0.000000
O -1.493280 1.073689 0.000000
O -1.170435 -1.166590 0.000000
H -2.979488 -0.258829 0.000000
H -0.498833 1.107195 0.000000
C 1.888896 0.179692 0.000000
O 1.493280 -1.073689 0.000000
O 1.170435 1.166590 0.000000
H 2.979488 0.258829 0.000000
H 0.498833 -1.107195 0.000000
}
I am trying to reproduce Lori’s Molpro 10 calculations for formic acid dimer in this paper: J. Chem. Theory Comput. 2014, 10, 49−57.
here is what I get from Molpro 18 and Psi4 for the DF-MP2/a5Z energies
paper | -379.14598836
molpro18 | -379.14598701
psi4 | -379.36355182
I am wondering if the RI basis sets in psi4 are the same as MP2FIT ones in Molpro, why Psi4 numbers do not agree with the other two. What is the underlying reason if it is not the basis set?
here is how my Psi4 input looks like:
=======Psi4 input=======================
molecule {
0 1
C -1.888896 -0.179692 0.000000
O -1.493280 1.073689 0.000000
O -1.170435 -1.166590 0.000000
H -2.979488 -0.258829 0.000000
H -0.498833 1.107195 0.000000
C 1.888896 0.179692 0.000000
O 1.493280 -1.073689 0.000000
O 1.170435 1.166590 0.000000
H 2.979488 0.258829 0.000000
H 0.498833 -1.107195 0.000000
}
Different auxiliary basis sets shouldn’t cause an error on the order of 0.2 kcal, let alone hartrees, for a system this size. You’d need @loriab to know for sure, but my hunch is that the difference is with the frozen core approximation. A quick skim of the methods section doesn’t mention the approximation either way, but it’s safe to assume the frozen core approximation is used if you see basis sets that look like pVXZ instead of pCVXZ. Psi does not invoke the frozen core approximation by default, but Molpro 10 does, and I imagine Molpro 18 does as well.