Q2DTor: A program to treat torsional anharmonicity through coupled pair torsions in flexible molecules

David Ferro-Costas, M. Natália D.S. Cordeiro, Donald G. Truhlar, Antonio Fernández-Ramos

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The Q 2DTor program (Quantum 2-Dimensional Torsions) is designed to calculate accurate rotational–vibrational partition functions (also called rovibrational partition functions) and thermodynamic functions for molecular systems having two [1] or more torsions. Systems with more than two torsions can also be studied by treating the torsions by pairs. The program searches for all the torsional conformers and evaluates the rovibrational partition function using the multi-structural harmonic oscillator (MS-HO) approximation and the extended two-dimensional torsion (E2DT) approximation. The latter incorporates full coupling of the two torsions by means of the two-dimensional non-separable (2D-NS) approximation [2], and it also includes their influence on the remaining degrees of freedom. The program also calculates the ideal gas-phase standard-state thermodynamic functions at the requested temperatures. Twenty molecules have been used to test Q 2DTor. Program summary: Program Title: Q2DTor Program Files doi: http://dx.doi.org/10.17632/wbgchgc2kp.1 Licensing provisions: GNU GPL v3 Programming language: Python 2.7 Nature of problem: Calculation of accurate partition functions and thermodynamic functions in molecular systems involving two torsional modes. Torsional anharmonicity is treated quantically and includes full coupling in the kinetic and potential energies between the torsions and between the torsions and the rest of the degrees of freedom. Solution method: The program uses the variational method to solve the Schrödinger equation of a two-dimensional torsional potential using Fourier series. All of the remaining degrees of freedom (non-torsional) are incorporated through a projected (the torsional modes are removed) rigid-rotator harmonic-oscillator partition function which is calculated at every torsional stationary point and that is allowed to vary with the torsional motion. The integration of the rovibrational partition function over the torsional space leads to a mixed quantum-classical vibrational partition function, which is transformed into a full quantum partition function by including the quantum contribution due to the torsions. For the evaluation of the integral, the rovibrational partition function at nonstationary points is carried out through a Delaunay triangulation procedure using the calculated rovibrational partition functions at the stationary points as nodes. Additional comments including Restrictions and Unusual features: The program is limited to two coupled torsional modes. References: [1] L. Simón-Carballido et al., J. Chem. Theory Comput. 13 (2017) 3478. [2] A. Fernández-Ramos, J. Chem. Phys. 138 (2013) 134112.

Original languageEnglish (US)
Pages (from-to)190-205
Number of pages16
JournalComputer Physics Communications
Volume232
DOIs
StatePublished - Nov 2018

Bibliographical note

Funding Information:
This work was partially supported by the Ministerio de Economia y Competitividad of Spain (Research Grant No. CTQ2014-58617-R), the Conseller?a de Cultura, Educaci?n e Ordenaci?n Universitaria (Axuda para Consolidaci?n e Estructuraci?n de unidades de investigaci?n competitivas do Sistema Universitario de Galicia, Xunta de Galicia ED431C 2017/17 & Centro singular de investigaci?n de Galicia and the European Regional Development Fund (ERDF), acreditaci?n 2016?2019, No. ED431G/09), the Funda??o para a Ci?ncia e a Tecnologia (FCT/MEC) through national funds, and cofinanced by the European Union (FEDER funds) under the Partnership Agreement PT2020, through projects No. UID/QUI/50006/2013 and No. POCI/01/0145/FEDER/007265 (LAQV@REQUIMTE), and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0015997. D.F.-C. also thanks Xunta de Galicia for financial support through a postdoctoral grant.

Funding Information:
This work was partially supported by the Ministerio de Economia y Competitividad of Spain (Research Grant No. CTQ2014-58617-R ), the Consellería de Cultura, Educación e Ordenación Universitaria (Axuda para Consolidación e Estructuración de unidades de investigación competitivas do Sistema Universitario de Galicia, Xunta de Galicia ED431C 2017/17 & Centro singular de investigación de Galicia and the European Regional Development Fund (ERDF), acreditación 2016–2019, No. ED431G/09 ), the Fundação para a Ciência e a Tecnologia (FCT/MEC) through national funds, and cofinanced by the European Union (FEDER funds) under the Partnership Agreement PT2020 , through projects No. UID/QUI/50006/2013 and No. POCI/01/0145/FEDER/007265 (LAQV@REQUIMTE), and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0015997 . D.F.-C. also thanks Xunta de Galicia for financial support through a postdoctoral grant.

Funding Information:
This work was partially supported by the Ministerio de Economia y Competitividad of Spain (Research Grant No. CTQ2014-58617-R), the Consellería de Cultura, Educación e Ordenación Universitaria (Axuda para Consolidación e Estructuración de unidades de investigación competitivas do Sistema Universitario de Galicia, Xunta de Galicia ED431C 2017/17 & Centro singular de investigación de Galicia and the European Regional Development Fund (ERDF), acreditación 2016–2019, No. ED431G/09), the Fundação para a Ciência e a Tecnologia (FCT/MEC) through national funds, and cofinanced by the European Union (FEDER funds) under the Partnership Agreement PT2020, through projects No. UID/QUI/50006/2013 and No. POCI/01/0145/FEDER/007265 (LAQV@REQUIMTE), and the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0015997. D.F.-C. also thanks Xunta de Galicia for financial support through a postdoctoral grant.

Publisher Copyright:
© 2018 Elsevier B.V.

Keywords

  • Coupled torsions
  • Hindered rotor
  • Partition function
  • Thermodynamic functions

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