Hello,
we are testing the SAPT electrostatic interaction between Na and Cl compared to a ESP computed at different methods (aug-cc-pvtz for all). The HF ESP of the Cl- interacting with a positive point charge probe at the corresponding distance yields -588.7 kj/mol for HF ( 590 for MP2 and is also comparable for CC), while SAPT0 electrostatics gives -608, which should be comparable to HF. The argument was that the interaction point charge model should give stronger interaction, but we are getting SAPT stronger by a margin.
Do you have any idea what could be the source of the discrepancy?
Hello,
The first thing I notice is the basis set, which for SAPT0 calculations should ALWAYS be jun-cc-pvdz. The performance of SAPT0 relies heavily on cancellation of errors, so jun-cc-pvdz must be used. Secondly, more information on your tests are required to examine this issue any further; for instance, what is the distance between the Cl- and the point charge? Can you post your input files?
From,
Mango
I do not agree. If someone wants to compare energies calculated with different methods, then the basis set should be the same. Otherwise you do not know whether the difference is caused by the method or by the basis set. Of course one can repeat these comparisons for different basis sets