The ORCA quantum chemistry program package

• Published in: The Journal of chemical physics Vol. 152; no. 22; pp. 224108 - 224125
• Main Authors: Neese, Frank, Wennmohs, Frank, Becker, Ute, Riplinger, Christoph
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 14.06.2020
• Subjects: Chemistry; Density functional theory; Magnetic properties; Quantum chemistry; Quantum mechanics; Solvation; Spectroscopy; Transition metals; Wave functions
• ISSN: 0021-9606; 1089-7690; 1089-7690
• DOI: 10.1063/5.0004608

In this contribution to the special software-centered issue, the ORCA program package is described. We start with a short historical perspective of how the project began and go on to discuss its current feature set. ORCA has grown into a rather comprehensive general-purpose package for theoretical research in all areas of chemistry and many neighboring disciplines such as materials sciences and biochemistry. ORCA features density functional theory, a range of wavefunction based correlation methods, semi-empirical methods, and even force-field methods. A range of solvation and embedding models is featured as well as a complete intrinsic to ORCA quantum mechanics/molecular mechanics engine. A specialty of ORCA always has been a focus on transition metals and spectroscopy as well as a focus on applicability of the implemented methods to “real-life” chemical applications involving systems with a few hundred atoms. In addition to being efficient, user friendly, and, to the largest extent possible, platform independent, ORCA features a number of methods that are either unique to ORCA or have been first implemented in the course of the ORCA development. Next to a range of spectroscopic and magnetic properties, the linear- or low-order single- and multi-reference local correlation methods based on pair natural orbitals (domain based local pair natural orbital methods) should be mentioned here. Consequently, ORCA is a widely used program in various areas of chemistry and spectroscopy with a current user base of over 22 000 registered users in academic research and in industry.