Comment on "Minimal Basis Iterative Stockholder: Atoms in Molecules for Force-Field Development"

TL;DR

This paper critically examines the MBIS method for atomic electron density partitioning, highlighting anomalies and issues in its original formulation to foster discussion and improvement.

Contribution

It identifies and discusses important anomalies in the MBIS method, providing a critical perspective to improve atomic population analysis techniques.

Findings

Reveals anomalies in the MBIS method's formulation

Highlights issues in the exponential function parameters

Calls for further discussion and refinement

Abstract

Verstraelen et al. (J. Chem. Theory Comput. 12 (2016) 3894-3912) recently introduced a new method for partitioning the electron density of a material into constituent atoms. Their approach falls within the class of atomic population analysis methods called stockholder charge partitioning methods in which a material electron distribution is divided into overlapping atoms. The Minimal Basis Iterative Stockholder (MBIS) method proposed by Verstraelen et al. composes the pro-atom density as a sum of exponential functions, where the number of exponential functions equals that element's row in the Periodic Table. Specifically, one exponential function is used for H and He, two for Li through Ne, three for Na through Ar, etc. In the MBIS method, the exponential functions parameters defining the pro-atom density are optimized in a self-consistent iterative procedure. Close examination reveals some important anomalies in the article by Verstaelen et al. The purpose of this comment article is to bring these important issues to readers' attention and to start a discussion of them.