Physical Principles of Constructing Hybrid QM/MM Procedures

Int J of Quantum Chemistry

2003

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ABSTRACT:The problem of substantiation of additive systematics such as molecular mechanics is considered. Antisymmetrized product of strictly localized geminals (APSLG) trial wavefunction is used as a starting point for this substantiation. The main force fields of molecular mechanics-those of bonding and bending-are derived for sp 3 carbon from the analysis of the total energy in semiempirical variant of the APSLG scheme. Analytically obtained constants of these force fields are in perfect coincidence with those typically used in the empirical force fields. The formulae for offdiagonal force fields are also obtained and analyzed. The application of the results for understanding the organic stereochemistry is discussed.

“…It was shown in Ref. 10 by analysis of the bond‐related contributions to the energy that there exist two parameters (functions of bond interatomic separation) for each bond ζ

_{−1}^{italicm}

and μ m describing, respectively, intrabond correlation and bond asymmetry. It was shown that for all chemical bonds these parameters are small.…”

Section: Bond Energy Equilibrium Bond Length and Bond Stretching Comentioning

confidence: 99%

Section: Bond Energy Equilibrium Bond Length and Bond Stretching Comentioning

confidence: 99%

Deductive molecular mechanics of sp³ carbon atom

Int J of Quantum Chemistry

2003

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“…(10)] tends to keep the interhybrid (and valence) angles at 90°, the other one [Eq. (9)] tends to place all substituents at the nitrogen atom to the plane. The observed pyramidal form is a result of the interplay between these two contributions.…”

Section: Stereochemistry and Molecular Mechanics Of Sp 3 Nitrogenmentioning

confidence: 99%

“…In past decades, progress in this field was enormous, which is shown in reviews [7][8][9]. At the same time the question about the interface between subsystems and the account of their interactions is not completely solved [9]. In practice, different recipes based on the intuitive models are used, and their success in description of that or another system is considered as an ultimate criterion on their value.…”

mentioning

confidence: 99%

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Deductive molecular mechanics of sp³ nitrogen atom and its application to analysis of a QM/MM interface

Int J of Quantum Chemistry

2004

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ABSTRACT:The antisymmetrized product of strictly localized geminals (APSLG) wave function is used to construct a mechanistic picture for the sp 3 nitrogen atom. We previously showed [18] that the classical force fields for the sp 3 carbon atom can be sequentially derived from the APSLG-MINDO/3 method. Here we try to extend this approach. Special attention is given to the hybridization pattern for the nitrogen atom. Interpolation formulae for the inversion potential are obtained and the role of different physical contributions to the local geometry structure around nitrogen is elucidated. The results obtained are applied to construction of the junction in QM/MM hybrid procedures when a lone pair is assigned to the QM subsystem while three covalent bonds are considered to be a part of the MM subsystem. Changes in the hybridization due to QM/MM boundary are considered as a source of modification of the QM lonepair characteristic as well as of that of the MM force fields.

Transferability of parameters of strictly local geminals' wave function and possibility of sequential derivation of molecular mechanics

2005

J Comput Chem

Abstract:The problem of substantiation of molecular mechanics (MM) remains actual due to growing popularity of hybrid quantum/classical (QM/MM) schemes. Recently proposed deductive molecular mechanics (DMM) seems to be a natural tool to derive mechanistic models of molecular energy (classical force fields) from a suitable quantum mechanical (QM) description of molecular structure. It is based on an assumption that the trial wave function underlying the MM description is one of the antisymmetrized product of strictly local geminals (SLG). A proof of transferability of electronic structure parameters (ESPs) in this approximation is an essential component of a logical framework for the transition from the QM to an MM description because it allows constructing expressions for potential energy surfaces by proper consideration of the response of the ESPs to the variations of geometry parameters. In the present article the ESPs defining density matrix elements and basis one-electron states (hybrid orbitals-HOs) in the SLG approximation are formally considered. The transferability of the density matrix elements with respect to the parameters of molecular electronic structure and the linear response relations for the HOs are proven to take place under very nonrestrictive conditions. Special attention is paid to numerical estimates of the ESPs' features giving an "experimental" support to approximate expressions for the molecular energy.