Semiempirical treatment of electrostatic potentials and partial charges in combined quantum mechanical and molecular mechanical approaches

Abstract

A semiempirical treatment of electrostatic potentials and partial charges is presented. These are the basic components needed for the evaluation of electrostatic interaction energies in combined quantum mechanical and molecular mechanical approaches. The procedure to compute electrostatic potentials uses AM1 and MNDO wave functions and is based on one previously suggested by Ford and Wang. It retains the NDDO approximation and is thus both easy to implement and computationally efficient. Partial atomic charges are derived from a semiempirical charge equilibration model, which is based on the principle of electronegativity equalization. Large sets of ab initio restricted Hartee‐Fock (RHF/6‐31G*) reference data have been used to calibrate the semiempirical models. Applying the final parameters (C, H, N, O), the ab initio electrostatic potentials are reproduced with an average accuracy of 20% (AM1) and 25% (MNDO), respectively, and the ab initio potential derived charges normally to within 0.1 e. In most cases our parameterized models are more accurate than the much more expensive quasi ab initio techniques, which employ deorthogonalized semiempirical wave functions and have generally been preferred in previous applications. © 1996 John Wiley & Sons, Inc.

Using a classical potential as an efficient importance function for sampling from an ab initio potential

“…The electronegativities and hardnesses of the atoms were taken to be constant during the simulation. We have used the Klopman-Ohno approximation as proposed by Bakowies and Thiel 33 for the calculation of the mixed terms in the hardness kernel…”

Molecular dynamics simulations of ion solvation by flexible‐boundary QM/MM: On‐the‐fly partial charge transfer between QM and MM subsystems

“…Due to the screening effect, the SS atoms that are further away from the boundary are deemed insignificantly affected by the partial charge transfer between the PS and SS, and they are thus not included in the FB treatments. The principle of electronic chemical potential equalization (also known as the principle of electronegativity equalization) has been applied to model the polarization and charge transfer in classical force fields . The works by Zhang and Lin have extended it to treat charge transfer between the quantum and classical subsystems.…”

Flexible-Boundary Quantum-Mechanical/Molecular-Mechanical Calculations: Partial Charge Transfer between the Quantum-Mechanical and Molecular-Mechanical Subsystems

“…A number of studies 1,2,16,[18][19][20][21][22][23][24][25][26][27][28][29][30][31] have been carried out to develop polarized-embedding QM/ MM schemes by combining the commonly used unpolarizable MM potentials (such as AMBER, 32 CHARMM, 33 and OPLS-AA [34][35][36][37][38][39] ) with classical polarization models. 19,[40][41][42][43][44][45][46][47][48][49][50][51][52] The basic idea is similar to reaction field theory, although the response is now given by a discrete model incorporating the atomic polarizability of individual SS atoms instead of by a continuum. Employing polarization models 19,[42][43][44] based on the principle of electronegativity equalization 53,54 to account for the flexibility of charge redistribution in the SS, we 31 recently developed the polarized...…”