Minimal Basis Iterative Stockholder Decomposition with Multipole Constraints.

Area of Science:

• Computational chemistry
• Molecular modeling
• Quantum chemistry

Background:

• The minimal basis iterative Stockholder (MBIS) method decomposes molecular electron densities into atomic quantities.
• MBIS-derived atomic charges often overestimate molecular dipole and quadrupole moments by approximately 10%.

Purpose of the Study:

• To develop a constrained MBIS model that accurately reproduces molecular dipole and quadrupole moments.
• To evaluate the performance of constrained atomic multipole moments in reproducing molecular electrostatic potentials (ESP) and assess their conformational dependence.

Main Methods:

• Implementing a constrained MBIS approach to enforce exact reproduction of molecular dipole and quadrupole moments.
• Comparing the accuracy of constrained and unconstrained atomic multipole moments in reproducing ESP.
• Analyzing the conformational dependence of constrained atomic multipole moments versus fitted atomic charges.

Main Results:

• A constrained MBIS model was successfully derived, ensuring atomic charges (or charges and dipoles) precisely match molecular dipole and quadrupole moments.
• Constrained atomic multipole moments demonstrated superior accuracy in reproducing the molecular ESP compared to unconstrained MBIS moments.
• The constrained procedure yielded atomic multipole moments with significantly lower conformational dependence than those obtained through ESP fitting.

Conclusions:

• The constrained MBIS method provides a robust approach for deriving accurate atomic multipole moments for force fields.
• This method improves the representation of molecular electrostatics and reduces artifacts associated with conformational variability.
• Constrained atomic multipole moments offer a more reliable and stable alternative to traditional ESP-fitted charges.