An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole...

Area of Science:

• Computational chemistry
• Materials science
• Solid-state physics

Background:

• Accurate modeling of intermolecular interactions is vital for predicting organic solid-state properties.
• Existing force fields often struggle to precisely describe crystal structures and energies, especially with complex organic molecules.

Purpose of the Study:

• To re-parameterize the exp-6 intermolecular force field for enhanced accuracy in the organic solid state.
• To incorporate atomic multipole electrostatics and account for induction effects using polarized electron densities.

Main Methods:

• Optimization of the exp-6 force field using atomic multipole electrostatics.
• Parameterization against 186 experimental low-temperature crystal structures and 53 sublimation enthalpies.
• Validation using a set of 129 organic molecular crystal structures.

Main Results:

• Re-parameterized force fields show improved reproduction of organic molecular crystal structures and lattice energies.
• Unit-cell dimensions were typically reproduced within 3% on the validation set.
• Lattice energies were systematically underestimated, with mean absolute errors between 7.4% and 9.0% compared to sublimation enthalpies.

Conclusions:

• The re-parameterized force field offers improved predictive power for organic crystal structures and energies.
• The inclusion of multipole electrostatics and polarization effects enhances the description of intermolecular forces.
• Further refinement may be needed to fully reconcile lattice energies with experimental sublimation enthalpies.