Spectroscopy and Scattering Studies Using Interpolated Ab Initio Potentials

Abstract

The Born–Oppenheimer potential energy surface (PES) has come a long way since its introduction in the 1920s, both conceptually and in predictive power for practical applications. Nevertheless, nearly 100 years later—despite astonishing advances in computational power—the state-of-the-art first-principles prediction of observables related to spectroscopy and scattering dynamics is surprisingly limited. For example, the water dimer, (H2O)2, with only six nuclei and 20 electrons, still presents a formidable challenge for full-dimensional variational calculations of bound states and is considered out of reach for rigorous scattering calculations. The extremely poor scaling of the most rigorous quantum methods is fundamental; however, recent progress in development of approximate methodologies has opened the door to fairly routine high-quality predictions, unthinkable 20 years ago. In this review, in relation to the workflow of spectroscopy and/or scattering studies, we summarize progress and challenges in the component areas of electronic structure calculations, PES fitting, and quantum dynamical calculations. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 72 is April 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Orthogonal State Reduction Variational Eigensolver for the Excited-State Calculations on Quantum Computers

“…Unfortunately, the scaling of the MC method is stiffly high on classical computers. 21,22 This motivates us to develop quantum algorithms to calculate excited states, especially the algorithms that can be implemented on NISQ devices.…”

“…Due to the multiconfigurational (MC) character of the electronic structures of excited states, MC quantum chemistry methods, such as CASPT2 and MRCISD, are required for the accurate excited-state calculations. Unfortunately, the scaling of the MC method is stiffly high on classical computers. , This motivates us to develop quantum algorithms to calculate excited states, especially the algorithms that can be implemented on NISQ devices.…”

New generalized potential energy function for diatomic systems

“…These approaches, strongly rely on the accuracy of first-principles calculations [19]. Despite the recent development of new and upgraded numerical approximations to solve the electronic problem, the state-of-theart ab initio methodologies are not extensively used in systems bearing atoms with relatively high atomic numbers (see for example [20,21]). In turn, spectroscopic measurements, essentially free of numerical constraints, provide accurate data for such systems.…”