Effective fragment potential method in Q-CHEM: A guide for users and developers

• Published in: Journal of computational chemistry Vol. 34; no. 12; pp. 1060 - 1070
• Main Authors: Ghosh, Debashree, Kosenkov, Dmytro, Vanovschi, Vitalii, Flick, Joanna, Kaliman, Ilya, Shao, Yihan, Gilbert, Andrew T.B., Krylov, Anna I., Slipchenko, Lyudmila V.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 05.05.2013; Wiley Subscription Services, Inc
• Subjects: Analytical chemistry; Cluster analysis; effective fragment potential; EFP library; Eulers equations; hybrid QM/MM; IQMOL; modular code; nonempirical force field; Q-CHEM; Quantum Theory; Software; Solvents - chemistry; WEBMO
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.23223

A detailed description of the implementation of the effective fragment potential (EFP) method in the Q‐CHEM electronic structure package is presented. The Q‐CHEM implementation interfaces EFP with standard quantum mechanical (QM) methods such as Hartree–Fock, density functional theory, perturbation theory, and coupled‐cluster methods, as well as with methods for electronically excited and open‐shell species, for example, configuration interaction, time‐dependent density functional theory, and equation‐of‐motion coupled‐cluster models. In addition to the QM/EFP functionality, a “fragment‐only” feature is also available (when the system is described by effective fragments only). To aid further developments of the EFP methodology, a detailed description of the C++ classes and EFP module's workflow is presented. The EFP input structure and EFP job options are described. To assist setting up and performing EFP calculations, a collection of Perl service scripts is provided. The precomputed EFP parameters for standard fragments such as common solvents are stored in Q‐CHEM's auxiliary library; they can be easily invoked, similar to specifying standard basis sets. The instructions for generating user‐defined EFP parameters are given. Fragments positions can be specified by their center of mass coordinates and Euler angles. The interface with the IQMOL and WEBMO software is also described. © 2013 Wiley Periodicals, Inc. The effective fragment potential (EFP) method is implemented in the Q‐CHEM electronic structure package. The implementation interfaces EFP with standard quantum mechanical methods such as Hartree–Fock, density functional theory, and coupled‐cluster models as well as with methods for electronically excited and open‐shell species.