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"Booth, George"
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School! : adventures at the Harvey N. Trouble Elementary School
Chronicles a week in the life of Ron Faster, whose famous parents are both seeking work, whose busdriver, Mr. Stuckinaditch, keeps making him late, and who must adjust to substitute teacher Mr. Don't-Know while Mrs. Petzgalore is away.
Book
Systematic Improvability in Quantum Embedding for Real Materials
Quantum embedding methods have become powerful tools to overcome the deficiencies of traditional quantum modeling in materials science. However, while these are systematically improvable in principle, in practice it is rarely possible to achieve rigorous convergence and often necessary to employ empirical parameters. Here, we formulate a quantum embedding theory, building on the methods of density-matrix embedding theory combined with local correlation approaches from quantum chemistry, to ensure the ability to systematically converge properties of real materials with accurate correlated wave-function methods controlled by a single, rapidly convergent parameter. By expanding supercell size, basis set, and the resolution of the fluctuation space of an embedded fragment, we show that the systematic improvability of the approach yields accurate structural and electronic properties of realistic solids without empirical parameters, even across changes in geometry. The results are presented in insulating, semimetallic, and more strongly correlated regimes, finding state-of-the-art agreement with experimental data.
Journal Article
Possum come a-knockin'
A cumulative tale in verse about a mysterious stranger that interrupts a family's daily routine.
Book
Towards an exact description of electronic wavefunctions in real solids
The properties of all materials arise largely from the quantum mechanics of their constituent electrons under the influence of the electric field of the nuclei. The solution of the underlying many-electron Schrödinger equation is a ‘non-polynomial hard’ problem, owing to the complex interplay of kinetic energy, electron–electron repulsion and the Pauli exclusion principle. The dominant computational method for describing such systems has been density functional theory. Quantum-chemical methods—based on an explicit ansatz for the many-electron wavefunctions and, hence, potentially more accurate—have not been fully explored in the solid state owing to their computational complexity, which ranges from strongly exponential to high-order polynomial in system size. Here we report the application of an exact technique, full configuration interaction quantum Monte Carlo to a variety of real solids, providing reference many-electron energies that are used to rigorously benchmark the standard hierarchy of quantum-chemical techniques, up to the ‘gold standard’ coupled-cluster ansatz, including single, double and perturbative triple particle–hole excitation operators. We show the errors in cohesive energies predicted by this method to be small, indicating the potential of this computationally polynomial scaling technique to tackle current solid-state problems.
Recent developments that reduce the computational cost and scaling of wavefunction-based quantum-chemical techniques open the way to the successful application of such techniques to a variety of real-world solids.
Quantum of solids
Computational descriptions of solid-state materials are currently dominated by methods based on density functional theory. An attractive and potentially more accurate approach would be to adopt the wavefunction-based methods of quantum chemistry, although these have not received as much attention because of the computational complexities involved. Now George Booth and colleagues show how recent developments that serve to reduce the computational cost and scaling of such quantum-chemical techniques open the way to their successful application to a variety of real-world solids.
Journal Article
Who invited you?
A rhyming counting tale in which Possum, Skunk, Frog, and other animals join a procession through the swamp, one with a potentially dangerous conclusion.
Book
Interpolating numerically exact many-body wave functions for accelerated molecular dynamics
While there have been many developments in computational probes of both strongly-correlated molecular systems and machine-learning accelerated molecular dynamics, there remains a significant gap in capabilities in simulating accurate non-local electronic structure over timescales on which atoms move. We develop an approach to bridge these fields with a practical interpolation scheme for the correlated many-electron state through the space of atomic configurations, whilst avoiding the exponential complexity of these underlying electronic states. With a small number of accurate correlated wave functions as a training set, we demonstrate provable convergence to near-exact potential energy surfaces for subsequent dynamics with propagation of a valid many-body wave function and inference of its variational energy whilst retaining a mean-field computational scaling. This represents a profoundly different paradigm to the direct interpolation of potential energy surfaces in established machine-learning approaches. We combine this with modern electronic structure approaches to systematically resolve molecular dynamics trajectories and converge thermodynamic quantities with a high-throughput of several million interpolated wave functions with explicit validation of their accuracy from only a few numerically exact quantum chemical calculations. We also highlight the comparison to traditional machine-learned potentials or dynamics on mean-field surfaces.
The wave function contains all the information about the electrons in chemical systems. Here, authors interpolate this quantum variable through chemical interactions, allowing us to follow the electronic state as atoms move and react.
Journal Article
Direct Comparison of Many-Body Methods for Realistic Electronic Hamiltonians
A large collaboration carefully benchmarks 20 first-principles many-body electronic structure methods on a test set of seven transition metal atoms and their ions and monoxides. Good agreement is attained between three systematically converged methods, resulting in experiment-free reference values. These reference values are used to assess the accuracy of modern emerging and scalable approaches to the many-electron problem. The most accurate methods obtain energies indistinguishable from experimental results, with the agreement mainly limited by the experimental uncertainties. A comparison between methods enables a unique perspective on calculations of many-body systems of electrons.
Journal Article
Never tease a weasel
Illustrations and rhyming text present animals in silly situations, such as a pig in a wig and a moose drinking juice, along with a reminder not to tease.
BOOK
A multi-resolution systematically improvable quantum embedding scheme for large-scale surface chemistry calculations
Predictive simulation of surface chemistry is critical in fields from catalysis to electrochemistry and clean energy generation. Ab-initio quantum many-body methods should offer deep insights into these systems at the electronic level but are limited by their steep computational cost. Here, we build upon state-of-the-art correlated wavefunctions to reliably reach ‘gold standard’ accuracy in quantum chemistry for extended surface chemistry. Efficiently harnessing graphics processing unit acceleration along with systematically improvable multi-resolution techniques, we achieve linear computational scaling up to 392 atoms. These large-scale simulations demonstrate the importance of converging to these extended system sizes, achieving consistency between simulations with different boundary conditions for the interaction of water on a graphene surface. We provide a benchmark for this water-graphene interaction that clarifies the preference for water orientations at the graphene interface. This is extended to the adsorption of carbonaceous molecules on chemically complex surfaces, including metal oxides and metal-organic frameworks, where we consistently achieve chemical accuracy compared to experimental references. This advances the simulation of molecular adsorption on surfaces, enabling reliable and improvable first-principles modeling of such problems by ab-initio quantum many-body methods.
Surfaces are the stage for vital catalytic reactions, but accurately simulating them is computationally expensive. Here, the authors introduce an efficient method using GPUs to model large, complex surfaces with exceptionally high, experiment-matching accuracy
Journal Article