Assuming I want to compute the atomization energy of methane with PyTorch which has an atomization energy of -0.631 Hartree. I compute the total energy with
eng = psi4.energy('b3lyp/6-311G(2DF,P)')
and I use the reference energies for the atoms in Hartree
By subtracting these reference energies I get an atomization energy of -0.687 Hartree which is a large difference to the expected result.
What am I missing?