Introducing Vmol software: A highly parallelized multi-purpose DFT program based on real-space grid formalism

We present a review of "Vmol," a highly parallelized, multi-purpose density functional theory (DFT) software based on a real-space grid formalism. By utilizing higher-order finite difference methods and nonlocal pseudopotentials, "Vmol" serves as a versatile and computationally robust platform for Kohn-Sham DFT calculations. By virtue of the hybrid parallel implementation (message passing interface/OpenMP), it delivers high performance on massively parallel computers integrating many processors. In the development of these several decades, "Vmol" offered marked adaptability as an electronic structure program to various extensions, such as the hybrid Quantum Mechanical (QM)/Molecular Mechanical (MM) approach and its combination with a theory of solutions (QM/MM-energy representation) based on statistical mechanics. We provide brief reviews of these methods as well as the important results obtained by their applications. "Vmol" was also utilized to implement kinetic energy and static correlation functionals formulated within the novel framework of DFT. The outline of the method will also be reviewed.