Exact non-additive kinetic potentials in realistic chemical systems

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Density functional theory (DFT) methods like frozen-density embedding theory require approximations for the non-additive kinetic potential, v(t)(nad)(r).
• v(t)(nad)(r) is a bifunctional, commonly approximated as v(t)(nad)[ρ(A),ρ(B)](r).

Purpose of the Study:

• To construct exact non-additive kinetic potentials (not bifunctionals) for chemically relevant electron density pairs.
• To analyze these exact potentials to inform the development of improved approximations for v(t)(nad)(r).

Main Methods:

• Construction of exact potentials for specific cases where ρ(A) is a one-electron or spin-compensated two-electron density.
• Utilizing Kohn-Sham molecular densities for ρ(A) and ρ(B).
• Analysis of the properties of the constructed exact potentials.

Main Results:

• Exact potentials were constructed for dissociating molecules, covalently bonded molecular fragments, and valence/core electron pairs.
• The analysis identified key properties that approximations must capture.
• The full von Weizsäcker kinetic energy component was found to be indispensable for accurate approximations.

Conclusions:

• Accurate approximations of the non-additive kinetic potential in DFT require careful consideration of specific electronic structure properties.
• The full von Weizsäcker component is essential for adequately approximating v(t)(nad)(r) for the studied density pairs.