arXiv subjects

Francesco Calcavecchia

Publications and source records attributed to Francesco Calcavecchia.

6 recordsLinked to original sources

arXiv2023

Static self energy and effective mass of the homogeneous electron gas from Quantum Monte Carlo calculations

We discuss the methodology of quantum Monte Carlo calculations of the effective mass based on the static self energy, $Σ(k,0)$. We then use variational Monte Carlo calculations of $Σ(k,0)$ of the homogeneous electron gas at various densities to obtain results very close to perturbative $G_0 W_0$ calculations for values of the density parameter $1 \le r_s \le 10$. The obtained values for the effective mass are close to diagrammatic Monte Carlo results and disagree with previous quantum Monte Carlo calculations based on a heuristic mapping of excitation energies to those of an ideal gas.

cond-mat.str-el↗

arXiv2021

Artificial Neural Networks as Trial Wave Functions for Quantum Monte Carlo

Inspired by the universal approximation theorem and widespread adoption of artificial neural network techniques in a diversity of fields, we propose feed-forward neural networks as a general purpose trial wave function for quantum Monte Carlo simulations of continous many-body systems. Whereas for simple model systems the whole many-body wave function can be represented by a neural network, the antisymmetry condition of non-trivial fermionic systems is incorporated by means of a Slater determinant. To demonstrate the accuracy of our trial wave functions, we have studied an exactly solvable model system of two trapped interacting particles, as well as the hydrogen dimer.

physics.comp-ph↗

arXiv2017

Two-Dimensional Hydrogen Structure at Ultra-High Pressure

We introduce a novel method that combines the accuracy of Quantum Monte Carlo simulations with ab-initio Molecular Dynamics, in the spirit of Car-Parrinello. This method is then used for investigating the structure of a two-dimensional layer of hydrogen at $T=0~\text{K}$ and high densities. We find that metallization is to be expected at $r_s \approx 1.1$, with an estimated pressure of $1.0\cdot10^3~a_0~\text{GPa}$, changing from a graphene molecular lattice to an atomic phase.

physics.comp-ph↗

arXiv2016

Metal-Insulator Transition of Solid Hydrogen by the Antisymmetric Shadow Wave Function

We revisit the pressure-induced metal-insulator-transition of solid hydrogen by means of variational quantum Monte Carlo simulations based on the antisymmetric shadow wave function. In order to facilitate studying the electronic structure of large-scale fermionic systems, the shadow wave function formalism is extended by a series of technical improvements, such as a revised optimization method for the employed shadow wave function and an enhanced treatment of periodic systems with long-range interactions. It is found that the superior accuracy of the antisymmetric shadow wave function results in a significantly increased transition pressure.

physics.comp-ph↗

arXiv2016

On the Fermion Sign Problem in Imaginary-Time Projection Continuum Quantum Monte Carlo with Local Interaction

We use the Shadow Wave Function formalism as a convenient model to study the fermion sign problem affecting all projector Quantum Monte Carlo methods in continuum space. We demonstrate that the efficiency of imaginary time projection algorithms decays exponentially with increasing number of particles and/or imaginary-time propagation. Moreover, we derive an analytical expression that connects the localization of the system with the magnitude of the sign problem, illustrating this prediction through some numerical results. Finally, we discuss the fermion sign problem computational complexity and methods for alleviating its severity.

physics.comp-ph↗

arXiv2014

On the Sign Problem of the Fermionic Shadow Wave Function

We present a whole series of novel methods to alleviate the sign problem of the Fermionic Shadow Wave Function in the context of Variational Monte Carlo. The effectiveness of our new techniques is demonstrated on the example of liquid 3He. We found that although the variance is substantially reduced, the gain in efficiency is restricted by the increased computational cost. Yet, this development not only extends the scope of the Fermionic Shadow Wave Function, but also facilitates highly accurate Quantum Monte Carlo simulations previously thought not feasible.

physics.comp-ph↗