arXiv subjects

Punit K. Jha

Publications and source records attributed to Punit K. Jha.

5 recordsLinked to original sources

arXiv2023

Massively parallel quantum chemistry: PFAS on over 1 million cloud vCPUs

Accurate solutions to the electronic Schrödinger equation can provide valuable insight for electron interactions within molecular systems, accelerating the molecular design and discovery processes in many different applications. However, the availability of such accurate solutions are limited to small molecular systems due to both the extremely high computational complexity and the challenge of operating and executing these workloads on high-performance compute clusters. This work presents a massively scalable cloud-based quantum chemistry platform by implementing a highly parallelizable quantum chemistry method that provides a polynomial-scaling approximation to full configuration interaction (FCI). Our platform orchestrates more than one million virtual CPUs on the cloud to analyze the bond-breaking behaviour of carbon-fluoride bonds of per- and polyfluoroalkyl substances (PFAS) with near-exact accuracy within the chosen basis set. This is the first quantum chemistry calculation utilizing more than one million virtual CPUs on the cloud and is the most accurate electronic structure computation of PFAS bond breaking to date.

physics.chem-ph↗

arXiv2020

Finite-temperature many-body perturbation theory in the grand canonical ensemble

A finite-temperature many-body perturbation theory is presented that expands in power series the electronic grand potential, chemical potential, internal energy, and entropy on an equal footing. Sum-over-states and sum-over-orbitals analytical formulas for the second-order perturbation corrections to these thermodynamic properties are obtained in a time-independent, nondiagrammatic, algebraic derivation, relying on the sum rules of the Hirschfelder-Certain degenerate perturbation energies in a degenerate subspace as well as nine algebraic identities for zeroth-order thermal averages of one- through four-indexed quantities and of products thereof. They reproduce numerically exactly the benchmark data obtained as the numerical derivatives of the thermal-full-configuration-interaction results for a wide range of temperature.

physics.chem-ph↗

arXiv2019

Finite-Temperature Many-Body Perturbation Theory in the Canonical Ensemble

Benchmark data are presented for the zeroth- through third-order many-body perturbation corrections to the electronic Helmholtz energy, internal energy, and entropy in the canonical ensemble in a wide range of temperature. They are determined as numerical $λ$-derivatives of the respective quantities computed by thermal full configuration interaction with a perturbation-scaled Hamiltonian, $\hat{H}=\hat{H}_0+λ\hat{V}$. Sum-over-states analytical formulas for up to the third-order corrections to these properties are also derived as analytical $λ$-derivatives. These formulas, which are verified by exact numerical agreement with the benchmark data, are given in terms of the Hirschfelder-Certain degenerate perturbation energies and should be valid for both degenerate and nondegenerate reference states at any temperature down to zero. The results in the canonical ensemble are compared with the same in the grand canonical ensemble.

physics.chem-ph↗

arXiv2019

Numerical Evidence Invalidating Finite-Temperature Many-Body Perturbation Theory

Low-order perturbation corrections to the electronic grand potential, internal energy, chemical potential, and entropy of a gas of noninteracting, identical molecules at a nonzero temperature are determined numerically as the $λ$-derivatives of the respective quantity calculated exactly (by thermal full configuration interaction) with a perturbation-scaled Hamiltonian, $\hat{H}_0 + λ\hat{V}$. The data thus obtained from the core definition of any perturbation theory serve as a benchmark against which analytical formulas can be validated. The first- and second-order corrections from finite-temperature many-body perturbation theory disagree with these benchmark data. This is because the theory neglects the variation of chemical potential with $λ$, thereby failing to converge at the exact, full-interaction ($λ=1$) limit, unless the exact chemical potential is known in advance. The renormalized finite-temperature perturbation theory [S. Hirata and X. He, J. Chem. Phys., 138, 204112 (2013)] is also found to be incorrect.

physics.chem-ph↗

arXiv2019

Converging finite-temperature many-body perturbation theory that conserves the average number of electrons

A finite-temperature perturbation theory for the grand canonical ensemble is introduced that expands chemical potential in a perturbation series and conserves the average number of electrons, ensuring charge neutrality of the system at each perturbation order. Two classes of (sum-over-state and reduced) analytical formulas are obtained in a straightforward, algebraic, time-independent derivation for the first-order corrections to chemical potential, grand potential, and internal energy, with the aid of several identities of the Boltzmann sums also introduced in this study. These formulas are numerically verified against benchmark data from thermal full configuration interaction. In the zero-temperature limit, the finite-temperature perturbation theory reduces analytically to and is consistent with the Møller-Plesset perturbation theory, but only for a nondegenerate ground state. For a degenerate ground state, its correct zero-temperature limit is not the Møller-Plesset perturbation theory, but the Hirschfelder-Certain degenerate perturbation theory.

physics.chem-ph↗