Constructing a non-additive non-interacting kinetic energy functional approximation for covalent bonds from exact...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Materials Science

Background:

• Accurate calculation of non-interacting kinetic energy (NAKE) is crucial for electronic structure methods.
• Existing approximations for NAKE face challenges, particularly for covalent bonds and stretched systems.

Purpose of the Study:

• To introduce a novel, non-decomposable approximation for NAKE, termed the covalent approximation (CA).
• To improve the accuracy of NAKE calculations for covalent bonds, especially in stretched configurations.
• To enhance the efficiency and accuracy of Partition-Density Functional Theory (P-DFT) calculations.

Main Methods:

• Developed the covalent approximation (CA) by combining the von Weizsäcker (vW) and Thomas-Fermi functionals.
• Utilized a switching function based on fragment densities to satisfy exact constraints.
• Incorporated ensembles and fractionally occupied spin-orbitals.
• Tested the CA within the framework of Partition-Density Functional Theory (P-DFT).

Main Results:

• The CA provides highly accurate NAKE values for stretched covalent bonds.
• CA outperforms standard NAKE approximations near equilibrium bond lengths.
• P-DFT calculations using CA are demonstrated to be both fast and accurate.

Conclusions:

• The covalent approximation (CA) offers a significant advancement in calculating NAKE for covalent bonds.
• CA enables more efficient and reliable P-DFT computations.
• This work paves the way for improved theoretical modeling in quantum chemistry and materials science.