# The use of constrained methods to analyze the molecular reactivity and to define a new type of pseudo atoms

## TL;DR

This paper introduces a new approach using constrained methods to study molecular reactivity and define pseudo atoms, which can simulate substituent effects in carbonyl molecules.

## Contribution

The paper proposes a novel definition of pseudo atoms based on population constraints and applies them to study molecular stability and reactivity.

## Key findings

- Pseudo atoms can simulate the inductive effect of substituents in carbonyl molecules.
- Constrained methods reveal insights into molecular reactivity and stability of complexes with water.
- The approach is implemented using constrained RHF computations with the STO-6G basis set.

## Abstract

Constrained methods in electronic structure methodologies add terms to the variational equations and generate solutions that represent distorted electronic distributions. In some cases, the new solutions can be used to study the chemical reactivity of parts of the molecule. Additionally, this contribution presents the use of population constraints to define pseudo atoms in a molecule. The effects of the pseudo atom on the molecular properties are analyzed. The pseudo atoms are used to simulate the inductive effect of the substituent in a group of carbonyl molecules and their effect on the stability of the complexes between these organic species and one molecule of water. A discussion on the assumptions involved in the present definition of pseudo atoms is also included.

The constrained RHF computations are done in a modified Hartree-Fock code for Gaussian basis sets. The selected basis set is STO-6 G.

The online version contains supplementary material available at 10.1007/s00894-024-06071-3.