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Polymorphism in 4'-hydroxyacetophenone: a molecular dynamics simulation study.

Carlos E S Bernardes¹, Manuel E Minas da Piedade, José N Canongia Lopes

¹Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Lisboa, Portugal. cebernardes@fc.ul.pt

The Journal of Physical Chemistry. B

|April 12, 2012

Summary

Molecular dynamics simulations reveal that simulating polarizability effects improves atomic point charge (APC) accuracy for 4′-hydroxyacetophenone (HAP) polymorphs. Combining flexible models with crystal-mimicking APCs best predicts energetic and volumetric properties.

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Area of Science:

Solid-state chemistry
Computational materials science
Crystallography

Background:

4′-hydroxyacetophenone (HAP) exists in two known polymorphs (form I, monoclinic; form II, orthorhombic).
Accurate modeling of lattice energetics is crucial for understanding solid-state behavior.
Previous simulations showed sensitivity to atomic point charge (APC) selection, asymmetric unit size (Z′), and molecular flexibility.

Purpose of the Study:

To develop an improved strategy for selecting atomic point charges (APCs) in molecular dynamics simulations.
To accurately predict the energetic and volumetric properties of HAP polymorphs.
To investigate the impact of molecular flexibility and APC methodology on simulation accuracy.

Main Methods:

Employed molecular dynamics (MD) simulations for HAP polymorphs.
Developed a new APC strategy simulating crystal lattice polarizability using the CHelpG methodology on crystal-like molecular aggregates.
Utilized both rigid and flexible molecular models to assess property prediction.

Main Results:

The new APC strategy, simulating polarizability, significantly improved energetic predictions compared to experimental values.
Flexible models combined with crystal-mimicking APCs yielded the best agreement for energetic and volumetric properties.
Volumetric properties showed less sensitivity to APC methodology when using flexible models.

Conclusions:

Simulating molecular polarizability within the crystal lattice is key for accurate APCs in MD simulations.
A combination of flexible molecular models and crystal-mimicking APCs provides superior prediction of HAP polymorph energetics and volumes.
The developed APC strategy offers a valuable tool for solid-state materials modeling.