Accurate Reference Data for the Nonadditive, Noninteracting Kinetic Energy in Covalent Bonds

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Accurate calculation of kinetic energy is crucial in electronic structure theory.
• Partition Density Functional Theory (PDFT) offers a framework for analyzing molecular fragments.
• Nonadditive, noninteracting kinetic energy (NAKE) is a key component in understanding fragment interactions.

Purpose of the Study:

• To numerically compute the NAKE for various diatomic molecular fragments.
• To compare different methods for treating fragment energies and densities within PDFT.
• To evaluate the accuracy of approximate kinetic energy functionals against exact numerical solutions.

Main Methods:

• Numerical calculation of NAKE using partition density functional theory (PDFT).
• Investigation of H2, Li2, Be2, C2, N2, F2, and Na2 fragments.
• Comparison of fractional orbital occupation and PDFT ensemble methods.
• Assessment of Thomas-Fermi and von Weizsäcker kinetic energy functionals.

Main Results:

• NAKE was successfully calculated for unique molecular fragments.
• The von Weizsäcker approximation was found to be nearly exact for NAKE in significant regions.
• Accurate NAKE predictions by the von Weizsäcker approximation were observed in stretched covalent bonds (Li2, Na2).

Conclusions:

• PDFT provides a robust method for calculating NAKE.
• The von Weizsäcker approximation is a promising tool for accurate NAKE calculations, particularly for stretched bonds.
• This work advances the understanding of kinetic energy contributions in molecular systems.