This manual describes version 3.4 of a code, MULTIMODE, which does Vibrational Self Consistent Field (VSCF) and several types of "CI" calculations for the rovibrational energies and wavefunctions of polyatomic molecules, transition states, clusters, etc. The code is based on the Watson Hamiltonian for non-linear molecules. (A version for linear molecules will be available soon.) The treatment is exact for zero and non-zero total angular momentum, J, and uses general potentials. For non-zero J, an approximate, adiabatic treatment of rotation can also be used. This approximate method, which is very efficient compared to an exact calculation, has been tested and should be very reliable for small values of J, except in those cases where there are strong Coriolis couplings.

The treatment of the potential is novel, and permits applications to many-mode systems. The potential is represented as an expansion in the number of simultaneously coupled modes. Currently this number can range from one to four. The computational effort increases significantly as this number increases; however, by doing calculations with increasing values of this number, convergence of this representation of the potential can be tested.