Composite and Low-Cost Approaches for Molecular Crystal Structure Prediction

Area of Science:

• Computational chemistry
• Materials science
• Crystallography

Background:

• Accurate and efficient lattice energy evaluation is crucial for molecular crystal structure prediction (CSP).
• Current high-accuracy methods like dispersion-corrected density-functional theory (DFT) are computationally expensive.
• Exploring cost-effective alternatives is essential for advancing CSP.

Purpose of the Study:

• To compare the performance of various low-cost computational methods for CSP.
• To identify reliable and efficient alternatives to high-cost DFT calculations.
• To establish a robust benchmarking strategy for evaluating CSP methods.

Main Methods:

• Evaluated DFT with numerical orbitals (SIESTA), empirical dispersion-corrected methods (HF-3c, PBEh-3c), and self-consistent-charge DFTB (SCC-DFTB3-D3).
• Investigated composite methods involving low-cost geometry optimization followed by high-accuracy single-point energy calculations (B86bPBE-XDM).
• Proposed the EE14 set for benchmarking relative lattice energies of chiral crystals.

Main Results:

• Assessing absolute lattice energies can be misleading; relative lattice energies are better performance indicators.
• The PBE-D2/DZP method with a B86bPBE-XDM single-point calculation demonstrated excellent performance at reduced cost.
• This multilevel method accurately reproduced the energy ranking for enantiopure and racemate forms of 1-aza[6]helicene.

Conclusions:

• Low-cost methods, particularly multilevel approaches, can achieve high accuracy in CSP.
• Relative lattice energy benchmarking is critical for method development in CSP.
• The B86bPBE-XDM//PBE-D2/DZP method shows promise for practical CSP applications, especially for chiral systems.