Quantum Monte Carlo Study Research Articles

Enhanced Pair-Density-Wave Vertices in a Bilayer Hubbard Model at Half Filling.

Motivated by the pair-density-wave (PDW) state found in the one-dimensional Kondo-Heisenberg chain, we report on a determinant quantum MonteCarlo study of pair fields for a two-dimensional half-filled Hubbard layer coupled to an itinerant, noninteracting layer with one electron per site. In a specific range of interlayer hopping, the pairing vertex associated with PDW order becomes more attractive than that for uniform d-wave pairing, although both remain subdominant to the leading antiferromagnetic correlations at half filling. Our result sheds light on where one potentially may find a PDW state in such a model.

First-principles quantum Monte Carlo study of charge-carrier mobility in organic molecular semiconductors

We present a first-principles numerical study of charge transport in a realistic two-dimensional tight-binding model of organic molecular semiconductors. We use the hybrid Monte Carlo (HMC) algorithm to simulate the full quantum dynamics of phonons and either single or multiple charge carriers without any tunable parameters. We introduce a number of algorithmic improvements, including efficient Metropolis updates for phonon fields based on analytical insights, which lead to negligible autocorrelation times and allow sub-per-mille precisions to be reached at a low computational cost of O(1) CPU hours. Our simulations produce charge-mobility estimates that are in good agreement with experiments and that also justify the phenomenological transient localization approach. Published by the American Physical Society 2024

Quantum Monte Carlo study of quantized muon in molecular systems

Quantum Monte Carlo study of quantized muon in molecular systems

4He monolayer on graphene: a quantum Monte Carlo study

We revisit the problem of adsorption of a single 4He layer on graphene, focusing on the commensurate (C 1/3) crystalline phase, specifically on whether it may possess a nonzero superfluid response, and on the existence of superfluid phases, either (metastable) liquid or vacancy-doped crystalline. We make use of canonical quantum Monte Carlo simulations at zero and finite temperature, based on a realistic microscopic model of the system. Our results confirm the absence of any superfluid response in the commensurate crystal, and that no thermodynamically stable uniform phase exists at lower coverage. No evidence of a possibly long-lived, metastable superfluid phase at C 1/3 coverage is found. Altogether, the results of ground-state projection methods and finite-temperature simulations are entirely consistent.

Continuous-time worm quantum Monte Carlo study of a two-dimensional spin-one XXZ model

Continuous-time worm quantum Monte Carlo study of a two-dimensional spin-one XXZ model

Quantum Monte Carlo study of thin parahydrogen films on graphite

The low-temperature properties of one and two layers of parahydrogen adsorbed on graphite are investigated theoretically through Quantum Monte Carlo simulations. We adopt a microscopic model that explicitly includes the corrugation of the substrate. We study the phase diagram of a monolayer up to second layer promotion, and the possible occurrence of superfluidity in the second layer. We obtain results down to a temperature as low as 8 mK. We find second-layer promotion to occur at a considerably greater coverage than obtained in previous calculations and estimated experimentally; moreover, we find no evidence of a possible finite superfluid response in the second layer, disproving recent theoretical predictions.

Quantum Monte Carlo and perturbative study of two-dimensional Bose-Fermi mixtures

Quantum Monte Carlo and perturbative study of two-dimensional Bose-Fermi mixtures

Calculating the Coulomb blockade phase diagram in the strong coupling regime of a single-electron transistor: a quantum Monte Carlo study

We present a novel approach for calculating the Coulomb blockade phase diagram (CBPD) in the experimentally accessible strong coupling regime of a single-electron transistor. Our method utilizes the path integral Monte Carlo technique to accurately compute the Coulomb oscillation of the differential capacitance (DC). Furthermore, we investigate the impact of the gate voltage and temperature variations on the DC, thereby gaining insights into the system’s behavior. As a result, we propose a method to calculate the Coulomb blockade boundary line and demonstrate its efficacy by setting the visibility parameter to 10%. The resulting boundary line effectively defines the transition between the Coulomb and non-Coulomb blockade regimes, thereby enabling the construction of a comprehensive CBPD.

Witnessing environment induced topological phase transitions via quantum Monte Carlo and cluster perturbation theory studies

Witnessing environment induced topological phase transitions via quantum Monte Carlo and cluster perturbation theory studies

Quantum Monte Carlo study of correlation energy and pair correlation function at various electron-positron density ratios: Accurate calculation of positron annihilation lifetimes in solids

Quantum Monte Carlo study of correlation energy and pair correlation function at various electron-positron density ratios: Accurate calculation of positron annihilation lifetimes in solids

Interplay of disorder and interactions in the bilayer band insulator: A determinant quantum Monte Carlo study

Interplay of disorder and interactions in the bilayer band insulator: A determinant quantum Monte Carlo study

Diffusion quantum Monte Carlo study on magnesium clusters as large as nanoparticles

Nanoscale magnesium clusters are important potential hydrogen storage materials, and density functional theory (DFT) is mainly used for their theoretical investigation. The results of the coupled-cluster theory at the singles and doubles level with a perturbative treatment of triples [CCSD(T)] were employed previously to choose proper exchange–correlation (XC) functionals in DFT calculations for magnesium clusters, but it is too expensive to be applied to Mgn with n > 7. The diffusion Monte Carlo (DMC) method is employed in this work to study magnesium clusters up to nanosize. The error of atomization energies with DMC using single-determinant-Jastrow (SDJ) trial wavefunctions has been shown to be somewhat larger than that of CCSD(T) for many molecules. However, cohesive energies with DMC using SDJ for Mgn with n ≤ 7 are in excellent agreement with those of CCSD(T) using the aug-cc-pVQZ basis set, with a difference of less than 1 kcal/mol. DMC results are employed to investigate the performance of different XC functionals on magnesium clusters. Our results indicate that the PBE0 functional is the best XC functional for determining the lowest-energy isomer when compared with DMC results, while the RPBE functional is the best XC functional for calculating cohesive energies per atom of these magnesium clusters with a mean absolute error of 0.5 kcal/mol. These XC functionals are expected to provide reasonable results for even larger magnesium clusters.

Erratum: Interacting lattice systems with quantum dissipation: A quantum Monte Carlo study [Phys. Rev. B 97 , 035148 (2018)

Erratum: Interacting lattice systems with quantum dissipation: A quantum Monte Carlo study [Phys. Rev. B <b>97</b> , 035148 (2018)

Quantum Monte Carlo study of semiconductor artificial graphene nanostructures

Quantum Monte Carlo study of semiconductor artificial graphene nanostructures

Influence of Coulomb blockade effect on the differential capacitance of two-island system: A quantum Monte Carlo study

Influence of Coulomb blockade effect on the differential capacitance of two-island system: A quantum Monte Carlo study

Quantum Monte Carlo study of Doppler broadening of positron annihilation radiation in semiconductors and insulators

Quantum Monte Carlo study of Doppler broadening of positron annihilation radiation in semiconductors and insulators

Quantum Monte Carlo study of superconductivity in rhombohedral trilayer graphene under an electric field

By using the constrained-phase quantum Monte Carlo method, we performed a systematic study of the ground state of the half filled Hubbard model for a trilayer honeycomb lattice. We analyze the effect of the perpendicular electric field on the electronic structure, magnetic property, and pairing correlations. It is found that the antiferromagnetism is suppressed by the perpendicular electric field, especially the long-range parts, and the dominant magnetic fluctuations are still antiferromagnetic. The electronic correlation drives a $d+id$ superconducting pairing to be dominant over other pairing patterns among various electric fields and interaction strengths. We also found that the $d+id$ pairing correlation is greatly enhanced as the on-site Coulomb interaction is increased. Our intensive numerical results may unveil the nature of the recently observed superconductivity in rhombohedral trilayer graphene under an electric field.

Quadriexciton Binding Energy in Electron–Hole Bilayers

Excitonic condensation and superfluidity have recently received a renewed attention, due to the fabrication of bilayer systems in which electrons and holes are spatially separated and form stable pairs known as indirect excitons. Dichalcogenides- and graphene-based bilayers are nowadays built and investigated, giving access to systems with (i) only spin degeneracy and (ii) spin and valley degeneracy. Simulation studies performed in the last decades at T=0 for simple, model electron–hole bilayers, as function of the interlayer distance and in-layer carrier density, have revealed in case (i) the formation of biexcitons in a tiny region of the parameter space and in case (ii) the formation of stable compounds made of four electrons and four holes (quadriexcitons) in a sizable region of the parameter space. Of some interest is the relation of the properties of isolated biexcitons (quadriexcitons) and those of their finite-density counterpart. In fact, the isolated biexciton has been repeatedly studied in the last years with simulations and other techniques. No simulations, instead, are available to our knowledge for the isolated quadriexciton, for which we present here results of the first quantum Monte Carlo (QMC) study. Stability with respect to the dissociation into biexcitons and the pair correlations while varying the interlayer distance d are discussed.

Quantum Monte Carlo study of the attractive kagome-lattice Hubbard model

Quantum Monte Carlo study of the attractive kagome-lattice Hubbard model

A Quantum Monte Carlo Study of the Structural, Energetic, and Magnetic Properties of Two-Dimensional H and T Phase VSe2.

Previous works have controversially claimed near-room-temperature ferromagnetism in two-dimensional (2D) VSe2, with conflicting results throughout the literature. These discrepancies in magnetic properties between both phases (T and H) of 2D VSe2 are most likely due to the structural parameters being coupled to the magnetic properties. Specifically, both phases have a close lattice match and similar total energies, which makes it difficult to determine which phase is being observed experimentally. In this study, we used a combination of density functional theory, highly accurate diffusion Monte Carlo (DMC), and a surrogate Hessian line-search optimization technique to resolve the previously reported discrepancy in structural parameters and relative phase stability. With DMC accuracy, we determined the free-standing geometry of both phases and constructed a phase diagram. Our findings demonstrate the successes of the DMC method coupled with the surrogate Hessian structural optimization technique when applied to a 2D magnetic system.