Employing Pseudopotentials to Tackle Excited-State Electron Spill-Out in Frozen Density Embedding Calculations

Area of Science:

• Computational chemistry
• Quantum mechanics
• Electronic structure theory

Background:

• Frozen density embedding (FDE) models environmental effects using embedding potentials.
• Existing FDE methods struggle with accurately representing Pauli repulsion, leading to charge spill-out in excited state calculations.
• This inaccuracy is particularly problematic when using diffuse basis functions.

Purpose of the Study:

• To improve the accuracy of frozen density embedding (FDE) for calculating excited states.
• To address the issue of charge spill-out in FDE calculations.
• To enhance the agreement between FDE and supermolecular calculations.

Main Methods:

• Incorporation of atomic all-electron pseudopotentials for environment atoms within the FDE framework.
• Application of the second-order algebraic diagrammatic construction (ADC(2)) scheme for vertical excitation energy calculations.
• Comparison of results with and without pseudopotentials, particularly when using diffuse basis functions.

Main Results:

• The inclusion of pseudopotentials significantly reduces charge spill-out in excited state calculations.
• Improved agreement between FDE and supermolecular calculations was observed.
• The mean absolute deviation (MAD) for vertical excitation energies decreased from 0.27 eV to 0.05 eV when diffuse functions were used.

Conclusions:

• Atomic pseudopotentials are an effective way to enhance the repulsive component of the FDE embedding potential.
• The proposed method improves the reliability of FDE for excited states in complex systems.
• This approach offers a more accurate and robust treatment of electron-nuclear attraction and Pauli repulsion.