Q-Chem is a general-purpose electronic structure package[1][2][3][4] featuring a variety of established and new methods implemented using innovative algorithms that enable fast calculations of large systems on various computer architectures, from laptops and regular lab workstations to midsize clusters, HPCC, and cloud computing using density functional and wave-function based approaches.

[6][8] The first lines of the Q-Chem code were written by Peter Gill, at that time a postdoc of Pople, during a winter vacation (December 1992) in Australia.

[6][8] Following a setback when Johnson left, the company became more decentralized, establishing and cultivating relationships with an ever-increasing circle of research groups in universities around the world.

The active Board of Directors currently consists of Lee, Mao, Faraji, Gill (past-President), Herbert, Krylov (President), and Hilary Pople (John's daughter).

[8] Q-Chem has been used as an engine in high-throughput studies, such as the Harvard Clean Energy Project,[9] in which about 350,000 calculations were performed daily on the IBM World Community Grid.

This transition, from in-house code to major electronic structure engine, has become possible due to contributions from numerous scientific collaborators; the Q-Chem business model encourages broad developer participation.

Q-Chem 5.2.2, released in December 2019, consists of 7.5 million lines of code, which includes contributions by more than 300 active developers (current estimate is 312).

Q-Chem can perform a number of general quantum chemistry calculations, such as Hartree–Fock, density functional theory (DFT) including time-dependent DFT (TDDFT), Møller–Plesset perturbation theory (MP2), coupled cluster (CC), equation-of-motion coupled-cluster (EOM-CC),[10][11][12] configuration interaction (CI), algebraic diagrammatic construction (ADC), and other advanced electronic structure methods.

The BrianQC plug-in speeds up Q-Chem calculations by taking advantage of GPUs on mixed architectures, which is highly efficient for simulating large molecules and extended systems.