Development of Embedded and Performance of Density Functional Methods for Molecular Crystals

Area of Science:

• Computational Chemistry
• Materials Science
• Solid-State Physics

Background:

• Periodic density functional theory (DFT) calculations with dispersion corrections are standard for studying molecular crystals.
• Existing methods can be computationally intensive, motivating the search for accurate and efficient alternatives.

Purpose of the Study:

• To introduce and evaluate an alternative quantum mechanical:quantum mechanical (QM:QM) method for molecular crystal calculations.
• To assess the performance of the QM:QM method against established periodic DFT methods, specifically BLYP+D3.
• To compare the accuracy of the QM:QM method with other dispersion-corrected methods like DFTB+D and DFT+D.

Main Methods:

• Development of a QM:QM approach by embedding BLYP+D3 into Density Functional Tight Binding (DFTB).
• Application of the QM:QM method to the X23 set of molecular crystals.
• Comparison of results with reference periodic BLYP+D3 calculations and other DFT-based methods.

Main Results:

• The developed QM:QM method closely reproduces reference periodic BLYP+D3 results.
• Lattice energies calculated by the QM:QM method are typically within 1-2% of BLYP+D3 values.
• Cell volumes obtained using the QM:QM method show excellent agreement, with deviations around 0.4% compared to BLYP+D3.

Conclusions:

• The proposed QM:QM method offers a computationally viable alternative to traditional periodic DFT calculations for molecular crystals.
• This method demonstrates high accuracy in predicting key structural and energetic properties.
• Further investigation into the comparative accuracy against DFTB+D and DFT+D is warranted.