Approaching the full configuration interaction ground state from an arbitrary wavefunction with gradient descent and...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Electronic Structure Theory

Background:

• Full Configuration Interaction (FCI) is an accurate but computationally expensive method for determining electronic structure.
• Standard FCI methods struggle with scaling to larger quantum systems due to high memory requirements.
• Optimizing wavefunctions from arbitrary reference states is crucial for advancing quantum chemistry calculations.

Purpose of the Study:

• To develop an efficient algorithm for optimizing FCI ground state wavefunctions.
• To overcome the memory limitations of traditional FCI approaches.
• To enable FCI energy calculations for larger and more complex quantum systems.

Main Methods:

• Utilizing gradient descent and quasi-Newton optimization algorithms.
• Evaluating energies via expectation values of an initial reference state $|0\rangle$.
• Avoiding the explicit storage of intermediate wavefunctions during optimization.

Main Results:

• Demonstrated that intermediate wavefunction energies can be computed without explicit storage.
• Enabled energy calculations for significantly larger systems than standard FCI methods.
• Successfully applied the algorithm using reference wavefunctions composed of non-orthogonal determinants.

Conclusions:

• The proposed optimization method offers a computationally feasible pathway to FCI energies.
• This technique significantly expands the size of quantum systems amenable to FCI calculations.
• The approach provides a practical tool for high-accuracy electronic structure investigations.