6,514 research outputs found
Benchmarking van der Waals Density Functionals with Experimental Data: Potential Energy Curves for H2 Molecules on Cu(111), (100), and (110) Surfaces
Detailed physisorption data from experiment for the H_2 molecule on low-index
Cu surfaces challenge theory. Recently, density-functional theory (DFT) has
been developed to account for nonlocal correlation effects, including van der
Waals (dispersion) forces. We show that the functional vdW-DF2 gives a
potential-energy curve, potential-well energy levels, and difference in lateral
corrugation promisingly close to the results obtained by resonant elastic
backscattering-diffraction experiments. The backscattering barrier is found
selective for choice of exchange-functional approximation. Further, the DFT-D3
and TS-vdW corrections to traditional DFT formulations are also benchmarked,
and deviations are analyzed.Comment: 15 pages, 9 figure
Ab initio molecular dynamics study of collective excitations in liquid HO and DO: Effect of dispersion corrections
The collective dynamics in liquid water is an active research topic
experimentally, theoretically and via simulations. Here, ab initio molecular
dynamics simulations are reported in heavy and ordinary water at temperature
323.15 K, or 50C. The simulations in heavy water were performed both
with and without dispersion corrections. We found that the dispersion
correction (DFT-D3) changes the relaxation of density-density time correlation
functions from a slow, typical of a supercooled state, to exponential decay
behaviour of regular liquids. This implies an essential reduction of the
melting point of ice in simulations with DFT-D3. Analysis of longitudinal (L)
and transverse (T) current spectral functions allowed us to estimate the
dispersions of acoustic and optic collective excitations and to observe the L-T
mixing effect. The dispersion correction shifts the L and T optic (O) modes to
lower frequencies and provides by almost thirty per cent smaller gap between
the longest-wavelength LO and TO excitations, which can be a consequence of a
larger effective high-frequency dielectric permittivity in simulations with
dispersion corrections. Simulation in ordinary water with the dispersion
correction results in frequencies of optic excitations higher than in DO,
and in a long-wavelength LO-TO gap of 24 ps (127 cm).Comment: 14 pages, 9 figure
First-principle study of paraelectric and ferroelectric CsHPO including dispersion forces: stability and related vibrational, dielectric and elastic properties
Using density functional theory (DFT) and density functional perturbation
theory (DFPT), we investigate the stability and response functions of
CsHPO, a ferroelectric material at low temperature. This material
cannot be described properly by the usual (semi-)local approximations within
DFT. The long-range e-e correlation needs to be properly taken into
account, using, for instance, Grimme's DFT-D methods, as investigated in this
work. We find that DFT-D3(BJ) performs the best for the members of the
dihydrogenated alkali phosphate family (KHPO, RbHPO,
CsHPO), leading to experimental lattice parameters reproduced with an
average deviation of 0.5 %. With these DFT-D methods, the structural,
dielectric, vibrational and mechanical properties of CsHPO are globally
in excellent agreement with the available experiments ( 2% MAPE for
Raman-active phonons). Our study suggests the possible existence of a new
low-temperature phase for CsHPO, not yet reported experimentally.
Finally, we report the implementation of DFT-D contributions to elastic
constants within DFPT.Comment: This paper was published in Physical Review B the 25 January 2017 (21
pages, 4 figures
Van der Waals density-functional theory study for bulk solids with BCC, FCC, and diamond structures
Proper inclusion of van der Waals (vdW) interactions in theoretical
simulations based on standard density functional theory (DFT) is crucial to
describe the physics and chemistry of systems such as organic and layered
materials. Many encouraging approaches have been proposed to combine vdW
interactions with standard approximate DFT calculations. Despite many vdW
studies, there is no consensus on the reliability of vdW methods. To help
further development of vdW methods, we have assessed various vdW functionals
through the calculation of structural prop- erties at equilibrium, such as
lattice constants, bulk moduli, and cohesive energies, for bulk solids,
including alkali, alkali-earth, and transition metals, with BCC, FCC, and
diamond structures as the ground state structure. These results provide
important information for the vdW-related materials research, which is
essential for designing and optimizing materials systems for desired physical
and chemical properties.Comment: 10 pages, 6 Figures, 3 Table
Vibrational and dielectric properties of the bulk transition metal dichalcogenides
Interest in the bulk transition metal dichalcogenides for their electronic,
photovoltaic, and optical properties has grown and led to their use in many
technological applications. We present a systematic investigation of their
interlinked vibrational and dielectric properties, using density functional
theory and density functional perturbation theory, studying the effects of the
spin-orbit interaction and of the long-range e- e correlation as part
of our investigation. This study confirms that the spin-orbit interaction plays
a small role in these physical properties, while the direct contribution of
dispersion corrections is of crucial importance in the description of the
interatomic force constants. Here, our analysis of the structural and
vibrational properties, including the Raman spectra, compare well to
experimental measurement. Three materials with different point groups are
showcased and data trends on the full set of fifteen existing hexagonal,
trigonal, and triclinic materials are demonstrated. This overall picture will
enable the modeling of devices composed of these materials for novel
applications.Comment: 11 pages, 6 figure
Mass Density Fluctuations in Quantum and Classical descriptions of Liquid Water
First principles molecular dynamics simulation protocol is established using
revised functional of Perdew-Burke-Ernzerhof (revPBE) in conjunction with
Grimme's third generation of dispersion (D3) correction to describe properties
of water at ambient conditions. This study also demonstrates the consistency of
the structure of water across both isobaric (NpT) and isothermal (NVT)
ensembles. Going beyond the standard structural benchmarks for liquid water, we
compute properties that are connected to both local structure and mass density
uctuations that are related to concepts of solvation and hydrophobicity. We
directly compare our revPBE results to the Becke-Lee-Yang-Parr (BLYP) plus
Grimme dispersion corrections (D2) and both the empirical fixed charged model
(SPC/E) and many body interaction potential model (MB-pol) to further our
understanding of how the computed properties herein depend on the form of the
interaction potential
Adsorption of imidazole on Au(111) surface: Dispersion corrected density functional study
We use density functional theory in the generalized gradient approximation to study the adsorption of imidazole on the Au(111) surface and account for dispersion effect using Grimme's empirical dispersion correction technique. Our results show that the adsorption energy of imidazole depends on the slab size and on the adsorption site. In agreement with other studies, we find the largest adsorption energy for imidazole on a top site of Au(111). However, we also note that the adsorption energy at other sites is substantial
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