A NEMO potential that includes the dipole-quadrupole and quadrupole-quadrupole polarizability

Area of Science:

• Computational chemistry
• Molecular modeling
• Quantum chemistry

Background:

• Molecular force fields are crucial for simulating molecular systems.
• Existing potentials like NEMO require systematic improvements for higher accuracy.
• Accurate intermolecular interactions are vital for understanding molecular behavior.

Purpose of the Study:

• To enhance the accuracy of the NEMO potential for the formaldehyde dimer.
• To investigate the impact of local quadrupole moments and higher-order polarizabilities on interaction potentials.
• To assess the performance of localized properties derived from MP2 densities compared to HF-SCF.

Main Methods:

• Systematic improvement of molecular force field terms.
• Introduction of local quadrupole moments and higher-order polarizabilities into the NEMO potential.
• Calculation and comparison of interaction energies using MP2 and HF-SCF methods.
• Analysis of localized properties based on MP2 and HF-SCF densities.

Main Results:

• Inclusion of quadrupole moments significantly improves the interaction potential of the formaldehyde dimer.
• Higher-order polarizabilities, up to quadrupole-quadrupole polarizability, provide a better description of intermolecular interactions.
• Localized properties derived from MP2 densities accurately reproduce BSSE-corrected MP2 interaction energies at large separations.
• HF-SCF based properties do not yield the same accuracy for interaction energies.

Conclusions:

• The enhanced NEMO potential with local quadrupole moments and higher-order polarizabilities offers improved accuracy for formaldehyde dimer interactions.
• MP2-based localized properties are effective for describing intermolecular interactions at larger distances.
• This work provides a pathway for developing more accurate molecular force fields through systematic term improvement.