EQMO: Equation of motion method for efficient electronic structure calculations

Equation of motion method has proven efficient for electronic structure calculations of very large systems, i.e. containing several million atoms. In this work, we redesign its previously published implementation and hereby release a revised software tool, EQMO, now capable of solving a crystalline TiO2 test sample of nearly a quarter of a billion atoms on NEC SX-Aurora TSUBASA vector computer. The legacy code has been rewritten in modern free-form Fortran, and the main developments include MPI support and optimisations for parallel execution. The previous version of this program may be found at https://doi.org/10.1016/0010-4655(92)90011-M.