GAMESS

GAMESS (General Atomic and Molecular Electronic Structure System) is a general-purpose quantum chemistry software package designed to perform ab initio electronic structure calculations on molecules and molecular systems. It is used to compute molecular energies, optimize geometries, and predict a range of properties for small to medium-sized systems. The program is cross-platform, primarily used on UNIX-like systems, and is distributed free for academic use with accompanying documentation and user support.

GAMESS has a long development history and exists in two major branches, GAMESS-US and GAMESS-UK, maintained by different groups. The project is collaborative and continually extended by contributors from academic institutions around the world. The name refers to the family of programs rather than a single fixed implementation, and updates over the years have integrated new methods and features while preserving a common input and output style.

Methodology and capabilities: GAMESS provides self-consistent-field methods, including Hartree-Fock and density functional theory, and a wide range of post-HF approaches such as Møller–Plesset perturbation theory (MP2/MP3/MP4), configuration interaction, and coupled-cluster methods (for example CCSD and CCSD(T)). It also supports multireference techniques such as CASSCF and related methods. The software handles basis-set selection, effective core potentials, and various property calculations. It supports geometry optimization, frequency analysis, transition-state searches, and the computation of molecular properties such as dipole moments and, with appropriate modules, nuclear magnetic resonance shielding via gauge-including atomic orbitals (GIAO).

Usage and output: Users provide text-based input files describing the system, methods, basis sets, and computation options. GAMESS produces plain-text output with energies, optimized geometries, vibrational data, and property results. Parallel execution through MPI enables larger calculations on high-performance computing resources.