Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme.

Area of Science:

• Quantum chemistry
• Computational physics
• Materials science

Background:

• Photoinduced charge-transfer processes are fundamental to novel photovoltaic phenomena and devices.
• Accurate and computationally inexpensive ab initio methods for charge-transfer excitations are highly sought after.
• Existing methods require extension to effectively describe intermolecular charge-transfer excitations.

Purpose of the Study:

• To extend a previously developed ab initio approach for single and double excitations to describe intermolecular charge-transfer excitations.
• To develop a method that avoids variational collapse and maintains orthogonality between ground and excited states.
• To accurately calculate charge-transfer excitation energies for relevant molecular systems.

Main Methods:

• Decomposition of Hartree-Fock (HF) ground state orbitals into four subspaces: occupied donor, occupied acceptor, virtual donor, and virtual acceptor.
• Construction of a Slater determinant representing an electron transfer from donor to acceptor.
• Optimization of the hole and particle positions by minimizing the HF energy functional within their respective subspaces.

Main Results:

• The developed method successfully describes intermolecular charge-transfer excitations.
• The approach maintains excited state orthogonality to the ground state and avoids variational collapse.
• Calculated lowest charge-transfer excitation energies for tetracyanoethylene-hydrocarbon complexes were obtained.

Conclusions:

• The extended ab initio method provides an accurate and computationally efficient means to study intermolecular charge-transfer excitations.
• This work contributes to the development of advanced computational tools for photovoltaic research.
• The method's validation on test systems demonstrates its potential for broader applications in photochemistry and materials science.