A Near-Term Quantum Algorithm for Computing Molecular and Materials Properties based on Recursive Variational Series Methods

Determining properties of molecules and materials is one of the premier applications of quantum computing. A major question in the field is: how might we use imperfect near-term quantum computers to solve problems of practical value? We propose a quantum algorithm to estimate properties of molecules using near-term quantum devices. The method is a recursive variational series estimation method, where we expand an operator of interest in terms of Chebyshev polynomials, and evaluate each term in the expansion using a variational quantum algorithm. We test our method by computing the one-particle Green's function in energy domain and the autocorrelation function in time domain.Comment: 16+10 pages, 3 figures; comments welcom

G0W0G_0W_0 Ionization Potentials of First-Row Transition Metal Aqua Ions

We report computations of the vertical ionization potentials within the $GW$ approximation of the near-complete series of first-row transition metal (V-Cu) aqua ions in their most common oxidation states, i.e. V$^{3+}$, Cr$^{3+}$, Cr$^{2+}$, Mn$^{2+}$, Fe$^{3+}$, Fe$^{2+}$, Co$^{2+}$, Ni$^{2+}$, and Cu$^{2+}$. The $d$-orbital occupancy of these systems spans a broad range from $d^2$ to $d^9$. All the structures were first optimized at the density functional theory level using a large cluster of explicit water molecules that are embedded in a continuum solvation model. Vertical ionization potentials were computed with the one-shot $G_0W_0$ approach on a range of transition metal ion clusters (6, 18, 40, and 60 explicit water molecules) wherein the convergence with respect to the basis set size was evaluated using the systems with 40 water molecules. We assess the results using three different density functional approximations as starting points for the vertical ionization potential calculations, namely $G_0W_0$@PBE, $G_0W_0$@PBE0, and $G_0W_0$@r$^2$SCAN. While the predicted ground-state structures are similar with all three exchange-correlation functionals, the vertical ionization potentials were in closer agreement with the experiment when using the $G_0W_0$@PBE0 and $G_0W_0$@r$^2$SCAN approaches, with the r2SCAN based calculations being significantly less expensive. Computed bond distances and vertical ionization potentials for all structures were compared with available experimental data and are in good agreement

Mechanistic origins of accelerated hydrogenation of mixed alkylaromatics by synchronised adsorption over Rh/SiO2

Catalytic reactions of mixed substrates sometimes behave differently from those of individual substrates. For example, the hydrogenation of propylbenzene over Rh/SiO2 proceeds 120% faster in the presence of toluene. Such an acceleration effect does not agree with the well-accepted Langmuir–Hinshelwood reaction model. In this paper, we examined its mechanism experimentally and computationally. The hydrogenation experiment of vaporised aromatics confirmed that the acceleration was specific to the liquid phase with the isopropanol solvent. Direct adsorption measurements revealed that toluene adsorption synchronises with propylbenzene adsorption. Density functional theory calculations confirmed the associates of toluene and propylbenzene on the catalyst surface in the polar environment. The formation of associates increased the adsorption energy of toluene and decreased that of propylbenzene. Lowered adsorption energy reduces the activation barrier for catalytic reaction and intensifies the reaction rate beyond the Langmuir–Hinshelwood model prediction

Software for the frontiers of quantum chemistry:An overview of developments in the Q-Chem 5 package

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design

First-Principles Calculations of the Energy and Width of the ²A_u Shape Resonance in <i>p</i>‑Benzoquinone: A Gateway State for Electron Transfer

Quinones are versatile biological electron acceptors and mobile electron carriers in redox processes. We present the first ab initio calculations of the width of the ²A_u shape resonance in the <i>para</i>-benzoquinone anion, the simplest member of the quinone family. This resonance state located at 2.5 eV above the ground state of the anion is believed to be a gateway state for electron attachment in redox processes involving quinones. We employ the equation-of-motion coupled-cluster method for electron affinity augmented by a complex-absorbing potential (CAP-EOM-EA-CCSD) to calculate the resonance position and width. The calculated width, 0.013 eV, is in excellent agreement with the width of the resonant peak in the photodetachment spectrum, thus supporting the assignment of the band to resonance excitation to the autodetaching ²A_u state. The methodological aspects of CAP-EOM-EA-CCSD calculations of resonances positions and widths in medium-sized molecules, such as basis set and CAP box size effects, are also discussed

Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package.

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear-electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an "open teamware" model and an increasingly modular design

Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear-electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an "open teamware" model and an increasingly modular design