HO2 ROVIBRATIONAL EIGENVALUE STUDIES FOR NONZERO ANGULAR-MOMENTUM

An efficient parallel algorithm is reported for determining all bound rovibrational energy levels for the HO2 molecule for nonzero angular m omentum values, J=1, 2, and 3. Performance tests on the GRAY T3D indic ate that the algorithm scales almost linearly when up to 128 processor s are used. Sustained performance levels of up to 3.8 Gflops have been achieved using 128 processors for J=3. The algorithm uses a direct pr oduct discrete variable representation (DVR) basis and the implicitly restarted Lanczos method (IRLM) of Sorensen to compute the eigenvalues of the polyatomic Hamiltonian. Since the IRLM is an iterative method, it does not require storage of the full Hamiltonian matrix-it only re quires the multiplication of the Hamiltonian matrix by a vector. When the IRLM is combined with a formulation such as DVR, which produces a very sparse matrix, both memory and computation times can be reduced d ramatically. This algorithm has the potential to achieve even higher p erformance levels for larger values of the total angular momentum. (C) 1997 American Institute of Physics.