ParallelizationStrategy for Large-Scale Vibronic Coupling Calculations.

The vibronic coupling model of Köppel,Domcke, and Cederbaum is a powerful means to understand, predict,and analyze electronic spectra of molecules, especially those thatexhibit phenomena that involve breakdown of the Born–Oppenheimerapproximation. In this work, we describe a new parallel algorithmfor carrying out such calculations. The algorithm is conceptuallyfounded upon a “stencil” representation of the requiredcomputational steps, which motivates an efficient strategy for coarse-grainedparallelization. The equations involved in the direct-CI type diagonalizationof the model Hamiltonian are presented, the parallelization strategyis discussed in detail, and the method is illustrated by calculationsinvolving direct-product basis sets with as many as 17 vibrationalmodes and 130 billion basis functions. [ABSTRACT FROM AUTHOR]