Calculation of Rovibronic Energy Levels
In view of the many unusual features of the potential energy surfaces of both states an exact program to calculate the rovibronic levels from the surfaces was required. For this purpose, in collaboration with Prof Gabriel Balint-Kurti, an existing program was adapted for this work. A grid based method using Jacobi co-ordinates is used; for the basic methods see Offer et al and references therein. One of the more significant modifications is the inclusion of electronic orbital angular momentum, which changes the form of the both kinetic the kinetic and potential energy operators as described by Petrolongo.
Calculations were again performed on the Bristol Beowulf systems; here the cluster nature of these machines was taken advantage of by modifying the program to run in parallel. The grid based method allows each row of the Hamiltonian matrix to be calculated independently and thus easily split over computational nodes. The longest part of the calculation is usually the diagonalisation of this matix; this is done using routines from the ScaLAPACK library. Perhaps surprisingly (as this involves a significant amount of communication) this gives good results on both the cluster with fast (Myrinet) or slow (100 Mbps ethernet) interconnections.
A. R. Offer and G. G. Balint-Kurti, J. Chem. Phys., 101, 10416 (1994).
C. Petrolongo, J. Chem. Phys., 89, 1297 (1988).