Fully coupled six-dimensional calculations of rovibrational eigenstates of floppy four-atom molecules

A methodology for rigorous and efficient quantum 6D calculation of the vibration-rotation levels of floppy four-atom molecules is reviewed. The rovibrational Hamiltonian in the diatom-diatom Jacobi coordinates is employed. The distance between the diatomic centers of mass is discretized by means of the discrete variable representation (DVR). At each DVR point, a 5D Hamiltonian is diagonalized. The quasiadiabatic basis of the 5D eigenvectors reduces greatly the dimension of the final Hamiltonian matrix, allowing its direct diagonalization to give the rovibrational energy levels and wave functions. The methodology lends itself well to implementation on parallel computers.