Ab initio molecular crystal structures, spectra, and phase diagrams

Area of Science:

• Solid-state chemistry and physics
• Computational chemistry
• Materials science

Background:

• Molecular crystals are crucial in various fields, including pharmaceuticals, materials science, and geochemistry.
• Accurate theoretical modeling of molecular crystals has been computationally challenging.
• Traditional methods struggle to capture complex intermolecular interactions and many-body effects.

Purpose of the Study:

• To introduce and demonstrate the power of the embedded-fragment scheme for molecular crystal electronic structure calculations.
• To showcase the application of advanced ab initio methods to solid-state problems.
• To address outstanding problems in solid-state, high-pressure, and geochemistry.

Main Methods:

• The embedded-fragment scheme divides crystals into interacting monomers and dimers.
• Modern electronic structure methods (e.g., Møller-Plesset perturbation, coupled-cluster) are applied to these fragments.
• Calculations incorporate self-consistently determined crystalline electrostatic fields, accounting for many-body electrostatic, exchange, and dispersion interactions.

Main Results:

• Accurate prediction of various solid properties: energies, structures, phase transitions, and spectra (IR, Raman, inelastic neutron scattering).
• Successful modeling of complex systems like ice Ih, CO2 phases, and solid formic acid.
• Explanation of spectral features, such as the origin of peaks in inelastic neutron scattering spectra of ice Ih.

Conclusions:

• The embedded-fragment scheme provides a versatile, accurate, and efficient approach for studying molecular crystals.
• These methods can fundamentally change the role of computation in solid-state chemistry research.
• The approach enables first-principles understanding of diverse solid-state phenomena.