Tango-95. An electronic structure program for modeling chemisorption

Abstract

tango-95, an ab initio electronic structure program based in part on the disco program of Almlöf, is described, with emphasis on the two electron integral evaluation. The program was developed largely for calculations on systems containing many metal atoms for heterogeneous catalysis studies. The evaluation of electron repulsion integrals was optimized for systems containing clusters of atoms which model metal surfaces. We show that the McMurchie and Davidson method (J. Comput. Phys., 26 (1978) 218) is appropriate in this context and we describe our implementation of the method for scalar processors. This implementation minimizes memory operations, and also floating point operations for important cases. We also comment on other features of the program such as gradient calculation, convergence algorithms, calculation of correlation energy and parallelization.