The choice of MP2 energy from FNO-CCSD(T) computations

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1 year 2 months ago #1294 by bkwx97
The CCSD(T)-MP2 term combined with MP2/CBS is used across computational chemistry as a benchmark, or used in place where one cannot afford an extensive series of CCSD(T) computations to extrapolate to CBS. FNO-CCSD(T) produces 4 different MP2 energies. One in the full basis, one for the FNO basis, one for NAF basis, and then another one before the FNO-DF-CCSD iterations start. Which MP2 energy is the correct one to obtain the MP2 in CCSD(T) - MP2? 

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1 year 2 months ago #1295 by nagypeter
Assuming you will have an expression, like
FNO-CCSD(T)/XZ - DF-MP2/XZ + DF-MP2/CBS
the first "DF-MP2 energy" in the full virtual and auxiliary basis should be used for DF-MP2/XZ as this is the one that matches DF-MP2/CBS, if you compute the latter via calc=df-mp2.

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