negative ocupations numbers in a CASPT2 calculation (-1.06)

Subject:

if B is 1s22s22p1, what is Li?

Passfield:

Comments:
: Hi everyone : I made a calculation of the benzene excímer and i obtain negative occupation numbers. The active space was chosen correctly; i understand that it may be result of the accuracy of the numerical methods employed in the calculation, but a occupation number of -1.6, is a big mistake : below I submit my input file : //////////////////////////// : &GATEWAY : coord=benzene.xyz : basis=bdzr : Group= XYZ : &SEWARD : &SCF : &RASSCF : symmetry=2; : spin=1; : nactel=12 0 0; : INACtive=18 18; : Ras2=6 6; : ALTEr= 7; 1 17 19; 1 22 27; 1 23 28; 1 24 38; 2 22 28; 2 23 29; 2 24 39 : LumOrb : &CASPT2 : DENSity : natural : //////////////////////////// : //////////////////////////// : 24 : angstrom : C 0.699767 1.212032 1.800000 : C 1.399534 0.000000 1.800000 : C 0.699767 -1.212032 1.800000 : C -0.699767 -1.212032 1.800000 : C -1.399534 0.000000 1.800000 : C -0.699767 1.212032 1.800000 : C 1.399534 1.800000 -1.800000 : C 0.699767 0.587968 -1.800000 : C -0.699767 0.587968 -1.800000 : C -1.399534 1.800000 -1.800000 : C -0.699767 3.012032 -1.800000 : C 0.699767 3.012032 -1.800000 : H -1.240080 3.947882 -1.800000 : H -2.480160 1.800000 -1.800000 : H -1.240080 -0.347882 -1.800000 : H 1.240080 -0.347882 -1.800000 : H 2.480160 1.800000 -1.800000 : H 1.240080 3.947882 -1.800000 : H -1.240080 2.147882 1.800000 : H -2.480160 0.000000 1.800000 : H -1.240080 -2.147882 1.800000 : H 1.240080 -2.147882 1.800000 : H 2.480160 0.000000 1.800000 : H 1.240080 2.147882 1.800000 : /////////////////////////// : where bdzr is the Roos Augmented Double Zeta basis set, obtained of the website: https://bse.pnl.gov/bse/portal. I also understand that can be used a C2h symmetry group, but the point is find the source of the error and not the calculation itself. : so my question is, i´m doing something wrong? : thanks in advance!