Vibrational adaptive sampling configuration interaction.

Area of Science:

• Quantum chemistry
• Molecular spectroscopy
• Computational physics

Background:

• Selected configuration interaction plus perturbation theory are established methods for electronic and vibrational Schrödinger equations.
• Recent advancements in selection algorithms have primarily focused on electronic structure, with limited application to vibrational problems.

Purpose of the Study:

• To adapt the adaptive sampling configuration interaction (ASCI) method for calculating molecular vibrational excitations.
• To evaluate the accuracy and computational efficiency of the vibrational ASCI method.
• To demonstrate its applicability to larger molecular systems.

Main Methods:

• Adaptation of the adaptive sampling configuration interaction (ASCI) method for vibrational Schrödinger equation.
• Benchmarking against established high-accuracy methods for acetonitrile and ethylene oxide.
• Calculation of low-lying vibrational states for naphthalene.

Main Results:

• The vibrational ASCI method achieves accuracy comparable to existing high-accuracy approaches.
• The method requires only modest computational resources.
• Successfully calculated 128 lowest energy vibrational states for naphthalene (48 vibrational degrees of freedom).

Conclusions:

• The vibrational ASCI method offers a computationally efficient and accurate approach for determining molecular vibrational excitations.
• This method shows significant potential for studying vibrational dynamics in larger and more complex molecular systems.