Individual Correlations in Ensemble Density Functional Theory: State- and Density-Driven Decompositions without...

Area of Science:

• Quantum Chemistry
• Computational Physics
• Many-Electron Systems

Background:

• Density-driven (DD) correlation energy is specific to many-electron ensembles.
• Previous approximations may not fully account for DD effects.
• Accurate correlation energy is vital for predicting molecular properties.

Purpose of the Study:

• Derive a general and simpler expression for DD correlation energy.
• Facilitate the development of improved approximations.
• Confirm the significance of DD effects in ensemble calculations.

Main Methods:

• Expression derived using ensemble weights and Kohn-Sham (KS) orbitals.
• Utilizes linear response of KS orbitals to ensemble weight variations.
• Avoids the need for additional state-driven KS systems.

Main Results:

• A general and simplified formula for DD correlation energy is presented.
• The evaluation of DD correlation energy is significantly simplified.
• The importance of DD effects is confirmed through the derived expression.

Conclusions:

• The derived expression offers a direct and promising route for approximations.
• This work simplifies the calculation of a crucial component of correlation energy.
• Enhanced accuracy in many-electron ensemble calculations is anticipated.