A state-specific multireference coupled-cluster method based on the bivariational principle | JoVE Visualize

Area of Science:

Quantum chemistry
Computational chemistry
Theoretical chemistry

Background:

Multireference coupled-cluster (MRCC) methods are crucial for accurately describing complex electronic structures.
Existing state-specific MRCC methods often face challenges with computational cost and complexity.
Arponen's bivariational principle offers a novel theoretical framework for developing new quantum chemical methods.

Purpose of the Study:

To introduce and formulate a new state-specific multireference coupled-cluster (MRCC) method based on Arponen's bivariational principle, termed bivariational MRCC (bivar-MRCC).
To assess the computational feasibility and accuracy of the bivar-MRCC method through pilot implementation and benchmark calculations.
To explore the potential of bivar-MRCC as a practical tool for a wider range of users in quantum chemistry.

Main Methods:

Development of the bivariational MRCC (bivar-MRCC) method, employing independent parameterizations for the wave function (ket) and its complex conjugate (bra).
Incorporation of formal bra and ket references as bivariational parameters to mitigate reference bias.
Pilot implementation and extensive benchmark calculations on standard quantum chemistry problems to validate the method's performance.

Main Results:

The bivar-MRCC method demonstrates manifest multiplicative separability of the state and additive separability of the energy.
The method preserves polynomial scaling of the working equations, contributing to its computational efficiency.
Benchmark calculations show that bivar-MRCC results are comparable to those obtained from established state-specific multireference methods.

Conclusions:

The bivariational MRCC (bivar-MRCC) method presents a computationally efficient and accurate approach for state-specific electronic structure calculations.
Its straightforward formulation and modest computational complexity make it a practical alternative to existing MRCC methods.
The bivar-MRCC method has the potential to become a valuable and accessible tool for researchers in computational and theoretical chemistry.