Split electrons in partition density functional theory.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Density Functional Theory

Background:

• Partition density functional theory (PDFT) is a computational method for fragmenting molecules.
• Minimizing fragment energies under density and electron constraints is key to PDFT.
• Handling non-integer electron populations in fragments is a challenge.

Purpose of the Study:

• To compare two methods for handling non-integer fragment electron populations in PDFT: ensemble (ENS) and fractional orbital occupation (FOO).
• To evaluate the performance of ENS and FOO on simple molecular systems.

Main Methods:

• Investigated a two-stage minimization procedure for PDFT.
• Implemented and compared the ensemble (ENS) approach and the fractional orbital occupation (FOO) approach.
• Applied both methods to models of heteronuclear diatomic molecules and actual diatomic molecules with two and four electrons.

Main Results:

• Both ENS and FOO yield identical total energies and electron densities.
• ENS fragment densities show less distortion compared to isolated fragments than FOO.
• ENS methods tend to preserve integer electron counts in fragments more effectively than FOO.
• FOO fragment dipoles provide an upper bound to ENS dipoles.

Conclusions:

• ENS is a more accurate representation of fragment electron distribution in PDFT compared to FOO.
• The choice of method impacts fragment density distortion and electron population representation.
• Understanding these differences is crucial for accurate molecular fragmentation studies.