Analysis of Density Functional Tight Binding with Natural Bonding Orbitals

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• The Density Functional Tight Binding (DFTB) model is an approximation for electronic structure calculations.
• Natural Bonding Orbitals (NBOs) provide insights into chemical bonding.
• Comparing DFTB with higher-level methods like Density Functional Theory (DFT) is crucial for assessing its accuracy.

Purpose of the Study:

• To analyze the chemical bonding descriptions provided by the DFTB model.
• To compare DFTB results with DFT (B3LYP/aug-cc-pVTZ) calculations using NBO analysis.
• To identify areas where DFTB requires improvement.

Main Methods:

• Analysis of chemical bonding using Natural Bonding Orbitals (NBOs).
• Comparison of DFTB3/3OB with B3LYP/aug-cc-pVTZ calculations.
• Investigation of diverse molecular systems including covalent, hypervalent, multicenter, and metal-ligand bonds.

Main Results:

• DFTB3/3OB generally provides physically sound descriptions of chemical bonding, showing agreement with DFT NBO properties.
• DFTB overestimates ligand-to-metal charge transfer and the ionic nature of pentavalent phosphate.
• Certain orbital interactions, like geminal interactions, are significantly overestimated by DFTB in hypervalent phosphates and transition metal compounds.

Conclusions:

• DFTB3/3OB is a reliable method for many bonding scenarios, but limitations exist.
• NBO analysis is valuable for pinpointing deficiencies in approximate quantum mechanical methods.
• The findings guide the systematic improvement of DFTB methods for electronic structure calculations.