gjf

GJF stands for Gaussian Job File, a plain text input format used by Gaussian, a family of computational chemistry programs. A GJF file encodes a complete calculation request for Gaussian, including the chosen method and basis set, the molecular geometry, and various calculation options. The format is commonly used to run calculations on local workstations and high performance computing clusters, and the file typically carries the .gjf or .com extension in practice.

File structure and content

A typical GJF file comprises several sections organized in a conventional order. It begins with resource directives, known as link0 commands, which may set memory and CPU usage (for example, lines starting with %mem and %nprocshared). After a blank line comes the route section, the first non-link0 line, which specifies the calculation type and methods (for example, a route like #P B3LYP/6-31G(d) Opt). Following another blank line is the title line(s), a line indicating the molecule’s charge and multiplicity (for example, 0 1), and then the geometry block listing atoms and their Cartesian coordinates. The file can also include optional sections or keywords for solvent models (SCRF), frequency analysis (Freq), constraints, or a checkpoint file (%chk) to restart calculations.

Usage and compatibility

GJF files are human-readable and editable with any text editor. They are widely supported across Gaussian versions (such as Gaussian 03, Gaussian 09, and Gaussian 16) and can be renamed with either .gjf or .com extensions depending on user conventions. While the basic structure remains consistent, specific versions may introduce minor differences or additional keywords. GJF remains a foundational format for documenting and sharing Gaussian calculations to ensure reproducibility.