The user documentation for Hibridon
BASISTYPE = 3
System subroutine: sy2pi
Basis subroutine: hiba03_2pi.F90
Ref. M. H. Alexander, J. Chem. Phys. 76, 5974 (1982); M. H. Alexander, Chem. Phys. 92, 337 (1985); G. C. Corey and M. H. Alexander, J. Chem. Phys. 85, 5652 (1986).
NTERM: (the number of potential surfaces involved: this should be 2 in this case). This parameter can not be changedNPAR: number of lambda-doublet components included
NPAR = 1, just ε = +1 states are includedNPAR ≠ 1, both ε = +1 and ε = -1 states are includedJMAX: maximum rotational quantum number minus 1/2IGU: inversion symmetry of states included in expansion
IGU = +1 for gerade states (for heteronuclear molecules IGUshould be +1)IGU = -1 for ungerade statesISA: nuclear permutation symmetry (s/a label) of states included in the expansion
If the flag IHOMO is .TRUE., then only s states will be included if ISA = +1 and only a states if ISA = -1
BROT: rotational constantASO : spin-orbit constantP, Q: lambda-doubling constats