Wavefunction in density functional theory embedding for excited states: which wavefunctions, which densities?

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Accurately modeling solvent effects is crucial for understanding chemical processes.
• Density functional theory (DFT) methods often struggle with differential polarization effects.
• State-specific embedding potentials offer a promising avenue for improvement.

Purpose of the Study:

• To analyze a novel wavefunction in DFT method for including differential polarization effects.
• To validate the supermolecular reference and assess embedding response using various wavefunction approaches.
• To investigate the impact of different functionals on excitation energy calculations.

Main Methods:

• Utilizing a recently proposed wavefunction in DFT method with state-specific embedding potentials.
• Employing quantum Monte Carlo (QMC), complete-active space second-order perturbation theory (CASPT2), and coupled cluster (CC) methods.
• Studying methylenecyclopropene and acrolein in water as test cases.

Main Results:

• QMC, CASPT2, and CC methods yielded consistent solvatochromic shifts and embedding responses.
• The proposed scheme corrects excitation energies from frozen environment calculations but can overshoot.
• Using wavefunction densities to polarize the environment ameliorates overshooting.
• Approximate kinetic-energy functionals significantly impact accuracy, more so than exchange-correlation functionals.

Conclusions:

• The developed method effectively incorporates differential polarization effects in DFT calculations.
• While improving upon frozen environment models, further refinement is needed to avoid overcorrection.
• The choice of kinetic-energy functional is critical for accurate excitation energy predictions in this approach.