A first-prototype multi-determinant X-ray constrained wavefunction approach: the X-ray constrained extremely...

Area of Science:

• Quantum chemistry
• Computational materials science
• Molecular modeling

Background:

• Current X-ray constrained wavefunction (XCW) methods rely on single-determinant wavefunctions.
• Investigating systems with multi-reference character requires advanced wavefunction approaches.

Purpose of the Study:

• To propose and validate a novel multi-determinant X-ray constrained wavefunction (XCW) technique.
• To apply the new method to determine resonance structure weights in naphthalene using experimental X-ray diffraction data.
• To compare results with traditional energy minimization methods.

Main Methods:

• Developed a multi-determinant XCW approach using a valence-bond-like expansion.
• Constructed determinants from localized molecular orbitals.
• Utilized experimental high-resolution X-ray diffraction data (structure factors).

Main Results:

• The multi-determinant XCW method was successfully applied to naphthalene.
• Calculated resonance structure weights at various temperatures.
• Observed significant differences in resonance weights compared to energy minimization alone.

Conclusions:

• The proposed multi-determinant XCW method is suitable for systems with multi-reference character.
• Explicitly including experimental structure factors provides crucial information for wavefunction determination.
• This approach offers a more accurate representation of electronic structure than energy minimization alone.