Double excitations from modified Hartree Fock subsequent minimization scheme.

Area of Science:

• Quantum Chemistry
• Theoretical Physics
• Computational Chemistry

Background:

• Doubly excited states are vital for technological applications like solar cells.
• Accurate ab initio description of doubly excited states is a significant theoretical challenge.
• Standard linear response theories fail to describe double excitations due to single Slater determinant limitations.

Purpose of the Study:

• To extend the existing Hartree-Fock (HF) approximation for singly excited states to calculate doubly excited states.
• To develop a computationally inexpensive ab initio method for describing double excitations.

Main Methods:

• The double excitation is modeled as two holes in occupied HF orbitals and two particles in virtual HF orbitals.
• Energy minimization determines the spin orbitals for holes and particles in respective subspaces.
• The extended HF approximation is applied to atoms, H2, and polyene molecules.

Main Results:

• Successfully extended the HF approximation to calculate doubly excited states.
• The method accurately describes excitations with significant double excitation character in test systems.
• The approach is demonstrated to be computationally inexpensive.

Conclusions:

• The developed ab initio method provides an accurate and efficient way to compute doubly excited states.
• This advancement has implications for improving theoretical models in areas like solar cell technology.
• The computationally inexpensive nature of the method makes it broadly applicable.