Electric multipole moments calculation with explicitly correlated coupled-cluster wavefunctions

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Accurate calculation of molecular dipole and quadrupole moments is essential for understanding molecular properties and interactions.
• Traditional methods can be computationally expensive, especially when high accuracy is required.
• Explicitly correlated methods offer a way to improve accuracy by including inter-electron distances in the wavefunction ansatz.

Purpose of the Study:

• To formulate and implement a computational method for calculating expectation values of dipole and quadrupole moments using the linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] model.
• To derive and implement an explicitly correlated version of the Λ equations within this framework.
• To assess the accuracy and efficiency of the developed method for molecular property calculations.

Main Methods:

• Formulation and implementation of a computational method based on the explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] model.
• Derivation and implementation of explicitly correlated Λ equations.
• Numerical tests on molecular systems to evaluate the accuracy of calculated dipole and quadrupole moments.

Main Results:

• The developed method provides accurate expectation values for dipole moments, achieving accuracy up to 0.01 a.u. at the double-ζ basis set level compared to the complete basis set limit.
• For quadrupole moments, the method yields results accurate up to 0.1 a.u. at the double-ζ level.
• With triple-ζ basis sets, the errors for quadrupole moments are reduced to below 0.01 a.u.

Conclusions:

• The implemented explicitly correlated coupled-cluster method offers a computationally efficient and accurate approach for calculating molecular dipole and quadrupole moments.
• The method demonstrates significant improvements in accuracy, particularly at smaller basis set sizes, reducing the computational cost for high-precision molecular property predictions.
• This advancement is valuable for various applications in computational chemistry and molecular physics requiring precise electric moments.