Hello,
we recently started to use PSI4 and are currently comparing results obtained with PSI4 with those obtained previously with other codes. While HF and DFT energies are usually identical within rounding errors, we realized that particularly CCSD and CCSD(T) energies deviated significantly.
One representative example is a simple CCSD/aug-cc-pvdz calculation of formaldehyde.
PSI4 reports the following energies:
HF energy -113.883953367912937
CCSD energy -114.236799942023211
A calculation with Gaussian09 results in the following values:
HF energy -113.8839534
CCSD energy -114.2319093
The psi4-Input looks like this:
memory 19 GB
molecule Test {
O 0.56196800 -1.26939800 0.00000000
C -0.24897300 -2.17498200 0.00000000
H -1.32371700 -1.96880100 0.00000000
H 0.12189300 -3.20325700 0.00000000
}
set basis aug-cc-pvdz
energy(‘CCSD’)
Do you have any suggestions on why these values deviate so much and how to overcome this problem?
Thank you very much for any suggestions.
Best wishes,
Martin