Ab Initio Electronic Structure Calculations by Auxiliary-Field Quantum Monte Carlo

Zhang, Shiwei

doi:10.1007/978-3-319-42913-7_47-1

Cited by 18 publications

(17 citation statements)

References 63 publications

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“…One is to allow the imposition of the constraints without incurring ergodicity problems 10,29,50 . The other is that, for groundstate or ZT calculations, it provides a clear and formal connection 28,51 with standard electronic structure methods within density-functional theory, which has enabled general computations in solids and molecular systems.…”

Section: Introductionmentioning

confidence: 99%

Finite-temperature auxiliary-field quantum Monte Carlo: Self-consistent constraint and systematic approach to low temperatures

Qin

Shi

et al. 2019

Phys. Rev. B

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We describe an approach for many-body calculations with a finite-temperature, grand canonical ensemble formalism using auxiliary-field quantum Monte Carlo (AFQMC) with a self-consistent constraint to control the sign problem. The usual AFQMC formalism of Blankenbecler, Scalapino, and Sugar suffers from the sign problem with most physical Hamiltonians, as is well known. Building on earlier ideas to constrain the paths in auxiliary-field space [Phys. Rev. Lett. 83, 2777(1999] and incorporating recent developments in zero-temperature, canonical-ensemble methods, we discuss how a self-consistent constraint can be introduced in the finite-temperature, grand-canonical-ensemble framework. This together with several other algorithmic improvements discussed here leads to a more accurate, more efficient, and numerically more stable approach for finite-temperature calculations. We carry out a systematic benchmark study in the two-dimensional repulsive Hubbard model at 1/8 doping. Temperatures as low as T = 1/80 (in units of hopping) are reached. The finite-temperature method is exact at very high temperatures, and approaches the result of the zero-temperature constrained-path AFQMC as temperature is lowered. The benchmark shows that systematically accurate results are obtained for thermodynamic properties.

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Section: Introductionmentioning

confidence: 99%

Finite-temperature auxiliary-field quantum Monte Carlo: Self-consistent constraint and systematic approach to low temperatures

Qin

Shi

et al. 2019

Phys. Rev. B

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“…A very recent review of AFQMC and its applications also to excited states can be found in Ref. [96].…”

Section: Alternatives To Diffusion Monte Carlomentioning

confidence: 99%

Excited-state calculations with quantum Monte Carlo

Feldt¹,

Filippi²

2020

Preprint

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Quantum Monte Carlo methods are first-principle approaches that approximately solve the Schrödinger equation stochastically. As compared to traditional quantum chemistry methods, they offer important advantages such as the ability to handle a large variety of many-body wave functions, the favorable scaling with the number of particles, and the intrinsic parallelism of the algorithms which are particularly suitable to modern massively parallel computers. In this chapter, we focus on the two quantum Monte Carlo approaches most widely used for electronic structure problems, namely, the variational and diffusion Monte Carlo methods. We give particular attention to the recent progress in the techniques for the optimization of the wave function, a challenging and important step to achieve accurate results in both the ground and the excited state. We conclude with an overview of the current status of excited-state calculations for molecular systems, demonstrating the potential of quantum Monte Carlo methods in this field of applications.

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“…Phaseless auxiliary-field quantum Monte Carlo (hereafter referred to as AFQMC) 52,53 is a systematically improvable stochastic electronic structure method which scales modestly with the fourth power of the system size in our current implementation. It has recently been shown to produce accurate triplet energies for all linear polyacenes with experimentally reported T1 energies (naphthalene through pentacene) as well as for biradicals.…”

Section: Introductionmentioning

confidence: 99%

In-Silico Prediction of Annihilators for Triplet Fusion Upconversion via Auxiliary-Field Quantum Monte Carlo

Weber

Churchill²,

Arthur³

et al. 2020

Preprint

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<div>The energy of the lowest-lying triplet state (T1) relative to the ground and first-excited singlet states (S0, S1) plays a critical role in optical multiexcitonic processes of organic chromophores. Focusing on triplet fusion upconversion, the S0 to T1 energy gap, known as the triplet energy, is difficult to measure experimentally for most molecules of interest. Ab initio predictions can provide a useful alternative, however</div><div>low-scaling electronic structure methods such as the Kohn-Sham and time-dependent variants of Density Functional Theory (DFT) rely heavily on the fraction of exact exchange chosen for a given functional, and tend to be unreliable when strong electronic correlation is present. Here, we apply auxiliary-field quantum Monte Carlo (AFQMC), a scalable electronic structure method capable of accurately describing even strongly correlated molecules, to predict the triplet energies for a series of candidate annihilators for triplet fusion (TF) upconversion, including 9,10 substituted anthracenes and substituted benzothiadiazole (BTD) and benzoselenodiazole (BSeD) compounds. We compare our results to predictions from a number of commonly used DFT functionals, as well as DLPNO-CCSD(T0), a localized approximation to coupled cluster with singles, doubles, and perturbative triples. Together with S1 estimates from absorption/emission spectra, which are well-reproduced by TD-DFT calculations employing the range-corrected hybrid functional CAM-B3LYP, we provide predictions regarding</div><div>the thermodynamic feasibility of upconversion by requiring a) the measured T1 of the sensitizer exceeds that of the calculated T1 of the candidate annihilator, and b) twice</div><div>the T1 of the annihilator exceeds its S1 energetic value. We demonstrate a successful example of in silico discovery of a novel annihilator, phenyl-substituted BTD, and present experimental validation of upconverted blue light emission when coupled to a platinum octaethylporphyrin (PtOEP) sensitizer. The BTD framework thus represents a new class of annihilators for TF upconversion. Its chemical functionalization, guided by the computational tools utilized herein, provides a promising route towards high energy (violet to near-UV) emission.</div>

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Ab Initio Electronic Structure Calculations by Auxiliary-Field Quantum Monte Carlo

Cited by 18 publications

References 63 publications

Finite-temperature auxiliary-field quantum Monte Carlo: Self-consistent constraint and systematic approach to low temperatures

Finite-temperature auxiliary-field quantum Monte Carlo: Self-consistent constraint and systematic approach to low temperatures

Excited-state calculations with quantum Monte Carlo

In-Silico Prediction of Annihilators for Triplet Fusion Upconversion via Auxiliary-Field Quantum Monte Carlo

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