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Calculation of Wave-functions with Frozen Orbitals in Mixed Quantum Mechanics/Molecular Mechanics methods. I. Application of the Huzinaga Equation.

Ferenczy, György G. (2013) Calculation of Wave-functions with Frozen Orbitals in Mixed Quantum Mechanics/Molecular Mechanics methods. I. Application of the Huzinaga Equation. Journal of Computational Chemistry, 34. pp. 854-861. ISSN 0192-8651

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Abstract

Mixed quantum mechanics/quantum mechanics (QM/QM) and quantum mechan- ics/molecular mechanics (QM/MM) methods make computations feasible for extended chemical systems by separating them into subsystems that are treated at different level of sophistication. In many applications the subsystems are covalently bound and the use of frozen localized orbitals at the boundary is a possible way to separate the sub- systems and to ensure a sensible description of the electronic structure near to the boundary. A complication in these methods is that orthogonality between optimized and frozen orbitals has to be warranted and this is usually achieved by an explicit or- thogonalization of the basis set to the frozen orbitals. An alternative to this approach is proposed by calculating the wave-function from the Huzinaga-equation that guaranties orthogonality to the frozen orbitals without basis set orthogonalization. The theoreti- cal background and the practical aspects of the application of the Huzinaga equation in mixed methods is discussed. Forces have been derived to perform geometry opti- mization with wave-functions from the Huzinaga-equation. Various properties have been calculated applying the Huzinaga-equation for the central QM subsystem, repre- senting the environment by point charges and using frozen strictly localized orbitals to connect the subsystems. It is shown that a 2-3 bond separation of the chemical or physical event from the frozen bonds allows a very good reproduction (typically around 1 kcal/mol) of standard Hartree-Fock-Roothaan results. The proposed scheme provides an appropriate framework for mixed QM/QM and QM/MM methods.

Item Type: Article
Subjects: Q Science / természettudomány > Q1 Science (General) / természettudomány általában
Q Science / természettudomány > QD Chemistry / kémia
Q Science / természettudomány > QD Chemistry / kémia > QD02 Physical chemistry / fizikai kémia
Depositing User: Dr György G. Ferenczy
Date Deposited: 13 Jun 2013 07:58
Last Modified: 13 Jun 2015 23:15
URI: http://real.mtak.hu/id/eprint/5579

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