Dipole preserving and polarization consistent charges

Self Cite

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi-Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi-Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred.

Section: Computational Detailsmentioning

confidence: 99%

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

Isegawa

Gao

Truhlar

2011

Self Cite

“…In our implementation, these two-electron integrals are computed by a multipole expansion 59 and partial charges are calculated by the DPPC population analysis. 54 The functional form and methods used in the XPHF model are identical to those employed in the XP3P model, and only differ by parameters and the system of question.…”

Section: X-pol With Pmowmentioning

confidence: 99%

“…The PMO Hamiltonian has been successfully used to develop a quantum mechanical force field within the X-Pol framework for liquid water called XP3P. 35 In addition, we have employed an alternative population analysis for calculating partial charges, called the dipolepreserving polarization consistent (DPPC) charge method, 54 which reproduces the total molecular dipole moment of each monomer from quantum mechanical calculations, eliminating the need for the charge scaling parameter in previous X-Pol simulations. Finally, the model has been parameterized using experimental data not available at the time of the previous study, 8,9 and has employed the optimized H-F bond length of 0.930 Å.…”

Section: Introductionmentioning

confidence: 99%

Quantum mechanical force field for hydrogen fluoride with explicit electronic polarization

Mazack

Gao

2014

Self Cite

The explicit polarization (X-Pol) theory is a fragment-based quantum chemical method that explicitly models the internal electronic polarization and intermolecular interactions of a chemical system. X-Pol theory provides a framework to construct a quantum mechanical force field, which we have extended to liquid hydrogen fluoride (HF) in this work. The parameterization, called XPHF, is built upon the same formalism introduced for the XP3P model of liquid water, which is based on the polarized molecular orbital (PMO) semiempirical quantum chemistry method and the dipole-preserving polarization consistent point charge model. We introduce a fluorine parameter set for PMO, and find good agreement for various gas-phase results of small HF clusters compared to experiments and ab initio calculations at the M06-2X/MG3S level of theory. In addition, the XPHF model shows reasonable agreement with experiments for a variety of structural and thermodynamic properties in the liquid state, including radial distribution functions, interaction energies, diffusion coefficients, and densities at various state points.

“…In addition, we included in the procedure the capability to reproduce experimental molecular polarizability and its atomic decomposition according to the dipole interaction model. 74 We called this method the dipole preserving and polarization consistent (DPPC) charge model. 74 Specifically, the DPPC charge has two contributions, the Mulliken population charge q MP A and the residual charges q B A due to preservation of atomic s and p hybridization dipole moments:…”

Section: Iic the Xp3p Model For Liquid Watermentioning

confidence: 99%

“…70,71 Alternatively, partial atomic charges can be derived to rigorously reproduce the molecular moments to any order of accuracy from a Lagrangian multiplier procedure. Following the method proposed by Thole and van Duijnen 72 and extended by Swart and van Duijnen, 73 we applied the Lagrangian multiplier approach to semiempirical methods, 74 which are known to yield excellent molecular dipole moments in comparison with experiments. In this approach, both the total molecular dipole moment and the local atomic hybridization contributions of the approximate NDDO wave function are reproduced exactly.…”

Section: Iic the Xp3p Model For Liquid Watermentioning

confidence: 99%

Quantum mechanical force field for water with explicit electronic polarization

Han

Mazack

Zhang

et al. 2013

Self Cite

A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensed-phase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen-and hydrogen-containing compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a three-point charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with three-point-charge potential) model, is suitable for modeling both gas-phase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 10 6 self-consistent-field calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across biological ion channels through membranes. © 2013 AIP Publishing LLC.