Density-Functional Tight-Binding Combined with the Fragment Molecular Orbital Method.

Area of Science:

• Computational Chemistry
• Materials Science
• Biophysics

Background:

• Accurate and efficient computational methods are crucial for studying large molecular systems.
• Existing methods often face challenges in balancing accuracy and computational cost for large systems.

Purpose of the Study:

• To develop and validate the Fragment Molecular Orbital-Density Functional Tight-Binding (FMO-DFTB) method.
• To assess the accuracy and computational efficiency of FMO-DFTB for various molecular systems.
• To demonstrate the applicability of FMO-DFTB for extremely large-scale systems.

Main Methods:

• Developed energy and gradient calculations for self-consistent-charge density-functional tight-binding (SCC-DFTB) combined with the fragment molecular orbital (FMO) approach.
• Incorporated an optional a posteriori treatment for dispersion interactions.
• Evaluated performance on polypeptides, DNA segments, and a small protein.

Main Results:

• FMO-DFTB achieved total energy errors below 1 kcal/mol compared to full SCC-DFTB for a 2000-atom polyalanine system.
• Optimized structures showed root-mean-square deviations below 0.1 Å.
• The method exhibits near-linear scaling (O(N^1.2)) with system size.
• Achieved 94% parallelization efficiency on 128 CPU cores.
• Successfully performed geometry optimization on a fullerite cluster with over one million atoms.

Conclusions:

• FMO-DFTB offers a highly accurate and computationally efficient approach for large molecular systems.
• The method's scalability and parallelization efficiency make it suitable for tackling systems with millions of atoms.
• FMO-DFTB represents a significant advancement for computational studies in chemistry, materials science, and biophysics.