arXiv subjects

O. Lopez-Acevedo

Publications and source records attributed to O. Lopez-Acevedo.

4 recordsLinked to original sources

arXiv2014

Orbital-Free Density Functional Theory Implementation with the Projector Augmented-Wave Method

We present a computational scheme for orbital-free density functional theory (OFDFT) that simultaneously provides access to all-electron values and preserves the OFDFT linear scaling as a function of the system size. Using the projector augmented-wave method (PAW) in combination with real-space methods we overcome some obstacles faced by other available implementation schemes. Specifically, the advantages of using the PAW method are two fold. First, PAW reproduces all-electron values offering freedom in adjusting the convergence parameters and the atomic setups allow tuning the numerical accuracy per element. Second, PAW can provide a solution to some of the convergence problems exhibited in other OFDFT implementations based on Kohn-Sham codes. Using PAW and real-space methods, our orbital-free results agree with the reference all-electron values with a mean absolute error of 10~meV and the number of iterations required by the self-consistent cycle is comparable to the KS method. The comparison of all-electron and pseudopotential bulk modulus and lattice constant reveal an enormous difference, demonstrating that in order to assess the performance of OFDFT functionals it is necessary to use implementations that obtain all-electron values. The proposed combination of methods is the most promising route currently available. We finally show that a parametrized kinetic energy functional can give lattice constants and bulk moduli comparable in accuracy to those obtained by the KS PBE method, exemplified with the case of diamond.

physics.comp-ph↗

arXiv2012

A multi-scale code for flexible hybrid simulations

Multi-scale computer simulations combine the computationally efficient classical algorithms with more expensive but also more accurate ab-initio quantum mechanical algorithms. This work describes one implementation of multi-scale computations using the Atomistic Simulation Environment (ASE). This implementation can mix classical codes like LAMMPS and the Density Functional Theory-based GPAW. Any combination of codes linked via the ASE interface however can be mixed. We also introduce a framework to easily add classical force fields calculators for ASE using LAMMPS, which also allows harnessing the full performance of classical-only molecular dynamics. Our work makes it possible to combine different simulation codes, quantum mechanical or classical, with great ease and minimal coding effort.

physics.comp-ph↗

arXiv2011

Electronic structure of Gold, Aluminum and Gallium Superatom Complexes

Using ab-initio computational techniques on crystal determined clusters, we report on the similarities and differences of Al$_{50}$(C$_5$(CH$_3)_5)_{12}$, Ga$_{23}$(N(Si(CH$_3)_{3}$)$_{2}$)$_{11}$, and Au$_{102}$(SC$_7$O$_2$H$_5$)$_{44}$ ligand-protected clusters. Each of the ligand-protected clusters in this study show the similar stable character which can be described via a electronic shell model. We show here that the same type of analysis leads consistently to derive a superatomic electronic counting rule, independently of the metal and ligand compositions. One can define the cluster core as the set of atoms where delocalized single-angular-momentum-character orbitals have hight weight using a combination of Bader analysis and the evaluation of Khon-Sham orbitals. Subsequently one can derive the nature of the ligand-core interaction. These results yield further insight into the superatom analogy for the class of ligand-protected metal clusters.

cond-mat.mes-hall↗

arXiv2008

Conductance through atomic point contacts between fcc(100) electrodes of gold

Electrical conductance through various nanocontacts between gold electrodes is studied by using the density functional theory, scalar-relativistic pseudopotentials, generalized gradient approximation for the exchange-correlation energy and the recursion-transfer-matrix method along with channel decomposition. The nanocontact is modeled with pyramidal fcc(100) tips and 1 to 5 gold atoms between the tips. Upon elongation of the contact by adding gold atoms between the tips, the conductance at Fermi energy E_F evolves from G ~ 3 G_0 to G ~ 1 G_0 (G_0 = 2e/h^2). Formation of a true one-atom point contact, with G ~ 1 G_0 and only one open channel, requires at least one atom with coordination number 2 in the wire. Tips that share a common vertex atom or tips with touching vertex atoms have three partially open conductance channels at E_F, and the symmetries of the channels are governed by the wave functions of the tips. The long 5-atom contact develops conductance oscillations and conductance gaps in the studied energy range -3 < E-E_F < 5 eV, which reflects oscillations in the local density of electron states in the 5-atom linear "gold molecule" between the electrodes, and a weak coupling of this "molecule" to the tips.

cond-mat.mtrl-sci↗