Hybridization-displaced charges for amino-acids: a new model using two point charges per atom along with bond-center charges

Abstract

A new charge distribution is proposed for the amino acids where each atom is associated with two point charges while each bond center is associated with one point charge. Centroids of charges arising due to atomic orbital hybridization called hybridization-displaced charges (HDC) and those located at the atomic sites and bond centers obtained by a modified form of the Mulliken scheme were combined. The density matrix calculations required for this analysis were performed at the B3LYP/6-31G** level of density functional theory. The combination of HDC centroids with the modified Mulliken charges was found to yield dipole moments and surface molecular electrostatic potentials (MEP) of the amino acids in good agreement with those obtained by rigorous DFT calculations or those obtained using the MEP-fitted CHelpG charges. This study shows that the combination of HDC centroids with the modified Mulliken charges is significantly superior to the conventional Mulliken charges.

Polyradicals of Polycyclic Aromatic Hydrocarbons as Finite Size Models of Graphene: Highly Open-Shell Nature, Symmetry Breaking, and Enhanced-Edge Electron Density

“…However, as discussed above, there are significant differences between the two types of systems from the point of view of negative MEP regions. Such regions would be preferentially involved in interactions with electrophiles. − In PAHs and their monoradicals, negative MEP regions with quite appreciable MEP magnitudes are fairly extended. However, in PAH polyradicals, negative MEP regions are localized near the sites where geometrical distortions are large.…”

“…The value of MEP (in a.u.) near a molecule at a point r is defined as italicV ( r ) = prefix∑ A Z A | R A − r | − ∫ ρ ( r ′ ) false| boldr − boldr ′ false| .25em normald boldr ′ where Z A and R A are atomic number and position vector of an atom A while ρ( r′ ) is continuous electron density at a point r′ . − MEP and molecular electric field (MEF) can be used as reliable descriptors of long-range intermolecular interactions, for example, hydrogen bonding. − The calculations were carried out using the Windows version of the Gaussian09 (G09W) suit of programs . The GaussView program (version 5.0) was used to plot continuous electron density and MEP maps and to visualize molecular structures and vibrational modes…”

Lowest Π–Π* electronic transitions in linear and two-dimensional polycyclic aromatic hydrocarbons: enhanced electron density edge effect

“…It is known that MEP and molecular electric field reveal features of electron density distribution as sensitive properties and can be used to predict chemical reactivity qualitatively [43][44][45][46][47][48][49]. Chemical hardness (η), defined as LUMO energy minus HOMO energy [50], was calculated for all the PAHs studied here.…”