34 research outputs found
Machine Learning-Driven Structure Prediction for Iron Hydrides
We created a computational workflow to analyze the potential energy surface
(PES) of materials using machine-learned interatomic potentials in conjunction
with the minima hopping algorithm. We demonstrate this method by producing a
versatile machine-learned interatomic potential for iron hydride via a neural
network using an iterative training process to explore its energy landscape
under different pressures. To evaluate the accuracy and comprehend the
intricacies of the PES, we conducted comprehensive crystal structure
predictions using our neural network-based potential paired with the minima
hopping approach. The predictions spanned pressures ranging from ambient to 100
GPa. Our results reproduce the experimentally verified global minimum
structures such as \textit{dhcp}, \textit{hcp}, and \textit{fcc}, corroborating
previous findings. Furthermore, our in-depth exploration of the iron hydride
PES at different pressures has revealed complex alterations and stacking faults
in these phases, leading to the identification of several new low-enthalpy
structures. This investigation has not only confirmed the presence of regions
of established FeH configurations but has also highlighted the efficacy of
using data-driven, extensive structure prediction methods to uncover the
multifaceted PES of materials
Averaging over atom snapshots in linear-response TDDFT of disordered systems: A case study of warm dense hydrogen
Linear-response time-dependent density functional theory (LR-TDDFT)
simulations of disordered extended systems require averaging over different
snapshots of ion configurations to minimize finite size effects due to the
snapshot--dependence of the electronic density response function and related
properties. We present a consistent scheme for the computation of the
macroscopic Kohn-Sham (KS) density response function connecting an average over
snapshot values of charge density perturbations to the averaged values of KS
potential variations. This allows us to formulate the LR-TDDFT within the
adiabatic (static) approximation for the exchange-correlation (XC) kernel for
disordered systems, where the static XC kernel is computed using the direct
perturbation method [Moldabekov et al., J. Chem. Theory Comput. 19, 1286
(2023)]. The presented approach allows one to compute the macroscopic dynamic
density response function as well as the dielectric function with a static XC
kernel generated for any available XC functional. The application of the
developed workflow is demonstrated for the example of warm dense hydrogen. The
presented approach is applicable for various types of extended disordered
systems such as warm dense matter, liquid metals, and dense plasmas
Assessing the accuracy of hybrid exchange-correlation functionals for the density response of warm dense electrons
We assess the accuracy of common hybrid exchange-correlation (XC) functionals
(PBE0, PBE0-1/3, HSE06, HSE03, and B3LYP) within Kohn-Sham density functional
theory (KS-DFT) for the harmonically perturbed electron gas at parameters
relevant for the challenging conditions of warm dense matter. Generated by
laser-induced compression and heating in the laboratory, warm dense matter is a
state of matter that also occurs in white dwarfs and planetary interiors. We
consider both weak and strong degrees of density inhomogeneity induced by the
external field at various wavenumbers. We perform an error analysis by
comparing to exact quantum Monte-Carlo results. In the case of a weak
perturbation, we report the static linear density response function and the
static XC kernel at a metallic density for both the degenerate ground-state
limit and for partial degeneracy at the electronic Fermi temperature. Overall,
we observe an improvement in the density response for partial degeneracy when
the PBE0, PBE0-1/3, HSE06, and HSE03 functionals are used compared to the
previously reported results for the PBE, PBEsol, LDA, AM05, and SCAN
functionals; B3LYP, on the other hand, does not perform well for the considered
system. Together with the reduction of self-interaction errors, this seems to
be the rationale behind the relative success of the HSE03 functional for the
description of the experimental data on aluminum and liquid ammonia at WDM
conditions
Transferable Interatomic Potentials for Aluminum from Ambient Conditions to Warm Dense Matter
We present a study on the transport and materials properties of aluminum
spanning from ambient to warm dense matter conditions using a machine-learned
interatomic potential (ML-IAP). Prior research has utilized ML-IAPs to simulate
phenomena in warm dense matter, but these potentials have often been calibrated
for a narrow range of temperature and pressures. In contrast, we train a single
ML-IAP over a wide range of temperatures, using density functional theory
molecular dynamics (DFT-MD) data. Our approach overcomes computational
limitations of DFT-MD simulations, enabling us to study transport and materials
properties of matter at higher temperatures and longer time scales. We
demonstrate the ML-IAP transferability across a wide range of temperatures
using molecular-dynamics (MD) by examining the thermal conductivity, diffusion
coefficient, viscosity, sound velocity, and ion-ion structure factor of
aluminum up to about 60,000 K, where we find good agreement with previous
theoretical data
Probing Iron in Earth's Core With Molecular-Spin Dynamics
Dynamic compression of iron to Earth-core conditions is one of the few ways
to gather important elastic and transport properties needed to uncover key
mechanisms surrounding the geodynamo effect. Herein a new machine-learned
ab-initio derived molecular-spin dynamics (MSD) methodology with explicit
treatment for longitudinal spin-fluctuations is utilized to probe the dynamic
phase-diagram of iron. This framework uniquely enables an accurate resolution
of the phase-transition kinetics and Earth-core elastic properties, as
highlighted by compressional wave velocity and adiabatic bulk moduli
measurements. In addition, a unique coupling of MSD with time-dependent density
functional theory enables gauging electronic transport properties, critically
important for resolving geodynamo dynamics.Comment: 3 Figures in main document, 8 Figures in the supplemental informatio
Data for "Dissociating the phononic, magnetic and electronic contributions to thermal conductivity: a computational study in α-iron"
This repository contains the data and script to generate the electronic component of the thermal conductivity in iron (alpha phase) relevant for the linked publication
Electrical Conductivity of Iron in Earth's Core from Microscopic Ohm's Law
Understanding the electronic transport properties of iron under high
temperatures and pressures is essential for constraining geophysical processes.
The difficulty of reliably measuring these properties under Earth-core
conditions calls for sophisticated theoretical methods that can support
diagnostics. We present results of the electrical conductivity within the
pressure and temperature ranges found in Earth's core from simulating
microscopic Ohm's law using time-dependent density functional theory. Our
predictions provide a new perspective on resolving discrepancies in recent
experiments
Data publication: Impact of electronic correlations on high-pressure iron: insights from time-dependent density functional theory
Simulation and literature data on the electrical and thermal conductivity of high-pressure iron. The raw simulation data was generated from time-dependent density functional theory calculations. Post-processing was applied to obtain the transport properties (conductivities) as described in the associated journal publication. The literature data was compiled from available publication data as referenced in the associated journal publication
Data publication: Assessing the accuracy of hybrid exchange-correlation functionals for the density response of warm dense electrons
This repository contains the DFT simulation results presented in the article "Assessing the accuracy of hybrid exchange-correlation functionals for the density response of warm dense electrons". The minimal dataset that would be necessary to interpret, replicate and build upon the findings reported in the article