Hasil untuk "physics.comp-ph"

Thomas D. Kühne

In a recent letter [T. D. Kühne, M. Krack, F. Mohamed and M. Parrinello, Phys. Rev. Lett. 98, 066401 (2007)], we outlined a new Car-Parrinello-like approach to Born-Oppenheimer molecular dynamics. Here, we provide a guide to performing actual calculations using our method and demonstrate this on liquid water at ambient conditions. We do not go into methodological details beyond those necessary for applying this approach, but focus on practical details pertinent to our particular implementation within the CP2K/Quickstep code [T. D. Kühne et al., J. Chem. Phys. 152, 194103 (2020)].

Tobias Dornheim, Jan Vorberger, Zhandos Moldabekov et al.

We present extensive new \emph{ab initio} path integral Monte Carlo (PIMC) results for the spin-resolved density response of the uniform electron gas (UEG) at warm dense matter conditions. This allows us to unambiguously assess the accuracy of previous theoretical approximations, thereby providing valuable new insights for the future development of dielectric schemes. From a physical perspective, we observe a nontrivial manifestation of an effective electron--electron attraction that emerges in the spin-offdiagonal static density response function at strong coupling, $r_s\gtrsim5$. All PIMC results are freely available online and can be used to benchmark new approximations and simulation schemes.

A. Berenguer, A. Coves, E. Bronchalo et al.

The resolution of the Green's function for obtaining the electrostatic potential generated by the charges located in the dielectric layer of a rectangular waveguide requires efficient integration techniques. Due to the characteristics and the oscillatory nature of the function to be integrated, the use of the Filon's method together with a convergence analysis is adequate. However, the application of this numerical integration technique can lead to numerical instabilities in the result. For this reason, in this research work we have presented two different methods to deal with these numerical errors of integration: SSA/MSSA and GPR. In this way it is possible to clean the electrostatic potential avoiding subsequent errors in the calculation of the electrostatic field.

Seungsoo Nam, Ryan J. McCarty, Hansol Park et al.

A Kohn-Sham (KS) inversion determines a KS potential and orbitals corresponding to a given electron density, a procedure that has applications in developing and evaluating functionals used in density functional theory. Despite the utility of KS inversions, application of these methods among the research community is disproportionately small. We implement the KS inversion methods of Zhao-Morrison-Parr and Wu-Yang in a framework that simplifies analysis and conversion of the resulting potential in real-space. Fully documented Python scripts integrate with PySCF, a popular electronic structure prediction software, and Fortran alternatives are provided for computational hot spots.

Takayuki Nishiyama, Atsuto Seko, Isao Tanaka

Accurate interatomic potentials are in high demand for large-scale atomistic simulations of materials that are prohibitively expensive by density functional theory (DFT) calculation. In this study, we apply machine learning potentials in a recently constructed repository to the prediction of the grain boundary energy in face-centered-cubic elemental metals, i.e., Ag, Al, Au, Cu, Pd, and Pt. The systematic application of machine learning potentials shows that they enable us to predict grain boundary structures and their energies accurately. The grain boundary energies predicted by the MLPs are in agreement with those calculated by DFT, although no grain boundary structures were included in training datasets of the present MLPs.

Michał Cieśla

Random sequential adsorption algorithm is a popular tool for modelling structure of monolayers built in irreversible adsorption experiments. However, this algorithm becomes very inefficient when the density of molecules in a layer rises. This problem has already been solved for a very limited range of basic shapes. This study presents a solution that can be used for any molecule occupying the surface that can be modelled by any number of different disks. Additionally, the presented algorithm stops when there is no possibility to add another shape to the monolayer. This allows to study properties of fully saturated, two-dimensional random packings built of complex shapes. For instance, the presented algorithm has been used to determine the mean saturated packing fractions of monolayers built of dimers and fibrinogen.

Marise J. E. Westbroek, Gil-Arnaud Coche, Peter R. King et al.

We present a path integral formulation of Darcy's equation in one dimension with random permeability described by a correlated multi-variate lognormal distribution. This path integral is evaluated with the Markov chain Monte Carlo method to obtain pressure distributions, which are shown to agree with the solutions of the corresponding stochastic differential equation for Dirichlet and Neumann boundary conditions. The extension of our approach to flow through random media in two and three dimensions is discussed.

Andrés Santos

Recently, Krüger and Vlugt [Phys. Rev. E 97, 051301(R) (2018)] have proposed a method to approximate an improper integral $\int_0^\infty \text{d}r\, F(r)$, where $F(r)$ is a given oscillatory function, by a finite-range integral $\int_0^L \text{d}r\, F(r) W(r/L)$ with an appropriate weight function $W(x)$. The method is extended here to an arbitrary (embedding) dimensionality $d$. A study of three-dimensional Kirkwood-Buff integrals, where $F(r)=4πr^2h(r)$, and static structure factors, where $F(r)=(4π/q) r\sin(qr) h(r)$, $h(r)$ being the pair correlation function, shows that, in general, a choice $d\neq 3$ (e.g., $d=7$) for the embedding dimensionality may significantly reduce the error of the approximation $\int_0^\infty \text{d}r\, F(r)\simeq \int_0^L \text{d}r\, F(r) W(r/L)$.

Zhijie Xu, Paul Meakin

A phase-field approach to the dynamics of liquid-solid interfaces that evolve due to precipitation and/or dissolution is presented. For the purpose of illustration and comparison with other methods, phase field simulations were carried out assuming first order reaction (dissolution/precipitation) kinetics. In contrast to solidification processes controlled by a temperature field that is continuous across the solid/liquid interface (with a discontinuous temperature gradient) precipitation/dissolution is controlled by a solute concentration field that is discontinuous at the solid/liquid interface. The sharp-interface asymptotic analysis of the phase-field equations for solidification [Karma and Rappel, Phys. Rev. E57 (1998) 4342] has been modified for precipitation/dissolution processes to demonstrate that the phase-field equations converge to the proper sharp-interface limit. The mathematical model has been validated for a one-dimensional precipitation/dissolution problem by comparison with the analytical solution.

Kim A. Nicoli, Pan Kessel, Michael Gastegger et al.

In this work, we extend the SchNet architecture by using weighted skip connections to assemble the final representation. This enables us to study the relative importance of each interaction block for property prediction. We demonstrate on both the QM9 and MD17 dataset that their relative weighting depends strongly on the chemical composition and configurational degrees of freedom of the molecules which opens the path towards a more detailed understanding of machine learning models for molecules.

G. Boyarsky, M. Ganz, R. Sterzel et al.

L. Johnson, T. Demeester

H. Irving, C. A. Gehring, R. Parish

J. Whitaker, R. Haugland, F. Prendergast

K. Toews, R. Shroll, C. Wai et al.

Feng Yan, S. Schubert, K. Mengel

Francesco Calcavecchia, Markus Holzmann

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.

A. Gennadios, A. H. Brandenburg, C. Weller et al.

A. Kingsbury, Oliver J.F. Foster, A. Nisbet et al.

M. Elsliger, R. Wachter, G. Hanson et al.