H2SOLV: Fortran solver for diatomic molecules in explicitly correlated exponential basis

We present the Fortran package H2SOLV for an efficient computation of the nonrelativistic energy levels and the wave functions of diatomic two-electron molecules within the Born-Oppenheimer approximation. The wave function is obtained as a linear combination of the explicitly correlated exponential (Kolos-Wolniewicz) functions. The computations of H2SOLV are performed within the arbitrary precision arithmetics, where the number of working digits can be adjusted by the user. The key part of H2SOLV is the implementation of the algorithm of an efficient computation of the two-center two electron integrals for arbitrary values of internuclear distances developed by one of us (Pachucki, 2013). This have been one of the long-standing problems of quantum chemistry. The code is parallelized, suitable for large-scale computations limited only by the computer resources available and can produce highly accurate results. As an example, we report several benchmark results obtained with H2SOLV, including the energy value accurate to 18 decimal digits. Program summary Program title: H2SOLV Catalogue identifier: AFBA_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AFBA_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 8740 No. of bytes in distributed program, including test data, etc.: 43089 Distribution format: tar.gz Programming language: Fortran 90. Computer: PCs or higher performance computers. Operating system: Linux / Unix. Has the code been vectorized or parallelized?: Yes RAM: From several Mbytes to several Gbytes, depending on the size of the basis. Classification: 2.1. External routines: MPFR library [2] and GMP library [3] need to be pre-installed on the computer. Nature of problem: Numerical solution of the two-center two-electron Schrodinger equation within the Born-Oppenheimer approximation using the explicitly correlated basis set of Kolos-Wolniewicz functions. Solution method: The method of solution is based on the algorithm developed in Ref. [1]. Running time: From seconds to days, depending on the size of the basis. The tests provided each take between 2 and 15 minutes to run. (C) 2016 Elsevier B.V. All rights reserved.