I have a molecule LiBH2 with C2V point group. I used 3-21G basis set and obtained RHF coefficients and symmetry of orbitals. I wish to find the set of orbitals (a,b,i,j)( where a and b are occupied and i and j are virtual oritals) that contribute to MP2 correlation energy. That is, in the process I have to find the non vanishing integrals. I tried finding and tried seeing what combination of MOs gives me A1 symmetry, because that will not vanish. However I am getting 156 such combinations which should not be the case. Can someone please help? I have been trying for really long now.
Thanks a lot in advance. Also, you feel this question is off-topic then please let me know where should I post this cause I have already tried it on chemistry.stackexchange.com