Using atomic charges to model molecular polarization

Zhu

Phys. Chem. Chem. Phys.

et al. 2023

Section: Introductionmentioning

confidence: 99%

Atomic charges in molecules defined by molecular real space partition into atomic subspaces

Zhu

Phys. Chem. Chem. Phys.

et al. 2023

J. Chem. Theory Comput.

“…, QTAIM and variations of the Hirshfeld method , ), or fitting to the electrostatic potential (ESP), , and these methods can be extended to atomic dipole and quadrupole moments. There is no unique choice for assigning atomic charges and multipole moments from a reference molecular electron density, but the present work is independent on how atomic charges are assigned, and the interested reader is referred to the other work for a more detailed discussion. , …”

Section: Introductionmentioning

confidence: 99%

“…It is well known that atomic charges, and atomic electric moments in general, depend on the position of other atoms, being in either the same or in different molecules, and this can be considered as intra-and intermolecular polarization. Different methods have been proposed to model molecular polarization by allowing exchange of charge between sites depending on the atomic positions, 1 and the connection between these models is the focus of the present work. Other popular methods for modeling the polarizability are the induced dipole model, where an atomic polarizability tensor accounts for induced dipole moments, and the Drude oscillator model, where the atomic charge is split between two sites connected by a spring.…”

Section: ■ Introductionmentioning

confidence: 99%

Unifying Charge-Flow Polarization Models

Jensen

2023

Self Cite

We show that several models where electric polarization in molecular systems is modeled by charge-flow between atoms can all be considered as different manifestations of a general underlying mathematical structure. The models can be classified according to whether they employ atomic or bond parameters and whether they employ atom/bond hardness or softness. We show that an ab initio calculated charge response kernel can be considered as the inverse screened Coulombic matrix projected onto the zero-charge subspace, and this may provide a method for deriving charge screening functions to be used in force fields. The analysis suggests that some models contain redundancies, and we argue that a parameterization of charge-flow models in terms of bond softness is preferable as it depends on local quantities and decay to zero upon bond dissociation, while bond hardness depends on global quantities and increases toward infinity upon bond dissociation.

J. Chem. Theory Comput.

“…For minor structural changes, the charge flow effect could be captured by using conformationally averaged electrostatics that attempt to describe the molecular electric field adequately for a range of conformers using a single, fixed electrostatic model with charges either located at the position of the nuclei or away from them. Alternatively, fluctuating charge models exist that assign nuclear charges dynamically in response to changes in distance to adjacent atoms based on atomic electronegativity and chemical hardness. − More recently, approaches have been developed to better describe the distortion of the molecular electric field with conformational change. For water, Piquemal and co-workers fitted multipole moments and charge-flow terms as a function of geometry, akin to earlier work for CO in myoglobin that employed a 3-site point charge and multipolar model with magnitudes that respond to bond length. , ML approaches have also been developed to predict multipole moments directly from molecular geometry and were recently used in a dynamics study .…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics with Conformationally Dependent, Distributed Charges

Boittier

Devereux

Meuwly

2022

Accounting for geometry-induced changes in the electronic distribution in molecular simulation is important for capturing effects such as charge flow, charge anisotropy, and polarization. Multipolar force fields have demonstrated their ability to correctly represent chemically significant features such as anisotropy and sigma holes. It has also been shown that off-center point charges offer a compact alternative with similar accuracy. Here, it is demonstrated that allowing relocation of charges within a minimally distributed charge model (MDCM) with respect to their reference atoms is a viable route to capture changes in the molecular charge distribution depending on geometry, i.e., intramolecular polarization. The approach, referred to as “flexible MDCM” (fMDCM), is validated on a number of small molecules and provides accuracies in the electrostatic potential (ESP) of 0.5 kcal/mol on average compared with reference data from electronic structure calculations, whereas MDCM and point charges have root mean squared errors of a factor of 2 to 5 higher. In addition, MD simulations in the NVE ensemble using fMDCM for a box of flexible water molecules with periodic boundary conditions show a width of 0.1 kcal/mol for the fluctuation around the mean at 300 K on the 10 ns time scale. For water, the equilibrium valence angle in the gas phase is found to increase by 2° for simulations in the condensed phase which is consistent with experiment. The accuracy in capturing the geometry dependence of the ESP together with the long-time stability in energy conserving simulations makes fMDCM a promising tool to introduce advanced electrostatics into atomistic simulations.