45 research outputs found

### Exchange and correlation effects in the relaxation of hot electrons in noble metals

We report extensive first-principles calculations of the inelastic lifetime
of low-energy electrons in the noble metals Cu, Ag, and Au. The quasiparticle
self-energy is computed with full inclusion of exchange and correlation (xc)
effects, in the framework of the GW\Gamma approximation of many-body theory.
Although exchange and correlation may considerably reduce both the screening
and the bare interaction of hot electrons with the Fermi gas, these corrections
have opposite signs. Our results indicate that the overall effect of
short-range xc is small and GW\Gamma linewidths are close to their xc-free
G^0W^0 counterparts, as occurs in the case of a free-electron gas.Comment: 9 pages, 8 figures. To appear in Phys. Rev.

### Benchmark Quantum Monte Carlo calculations of the ground-state kinetic, interaction, and total energy of the three-dimensional electron gas

We report variational and diffusion Quantum Monte Carlo ground-state energies
of the three-dimensional electron gas using a model periodic Coulomb
interaction and backflow corrections for N=54, 102, 178, and 226 electrons. We
remove finite-size effects by extrapolation and we find lower energies than
previously reported. Using the Hellman-Feynman operator sampling method
introduced in Phys. Rev. Lett. 99, 126406 (2007), we compute accurately, within
the fixed-node pproximation, the separate kinetic and interaction contributions
to the total ground-state energy. The difference between the interaction
energies obtained from the original Slater-determinant nodes and the
backflow-displaced nodes is found to be considerably larger than the difference
between the corresponding kinetic energies

### Momentum-space finite-size corrections for Quantum-Monte-Carlo calculations

Extended solids are frequently simulated as finite systems with periodic
boundary conditions, which due to the long-range nature of the Coulomb
interaction may lead to slowly decaying finite- size errors. In the case of
Quantum-Monte-Carlo simulations, which are based on real space, both real-space
and momentum-space solutions to this problem exist. Here, we describe a hybrid
method which using real-space data models the spherically averaged structure
factor in momentum space. We show that (i) by integration our hybrid method
exactly maps onto the real-space model periodic Coulomb-interaction (MPC)
method and (ii) therefore our method combines the best of both worlds
(real-space and momentum-space). One can use known momentum-resolved behavior
to improve convergence where MPC fails (e.g., at surface-like systems). In
contrast to pure momentum-space methods, our method only deals with a simple
single-valued function and, hence, better lends itself to interpolation with
exact small-momentum data as no directional information is needed. By virtue of
integration, the resulting finite-size corrections can be written as an
addition to MPC.Comment: 6 pages, 3 figures, submitted to Phys. Rev.

### Electron-hole and plasmon excitations in 3d transition metals: Ab initio calculations and inelastic x-ray scattering measurements

We report extensive all-electron time-dependent density-functional
calculations and nonresonant inelastic x-ray scattering measurements of the
dynamical structure factor of 3d transition metals. For small wave vectors, a
plasmon peak is observed which is well described by our calculations. At large
wave vectors, both theory and experiment exhibit characteristic low-energy
electron-hole excitations of d character which correlate with the presence of d
bands below and above the Fermi level. Our calculations, which have been
carried out in the random-phase and adiabatic local-density approximations, are
found to be in remarkable agreement with the measured dynamical structure
factor of Sc and Cr at energies below the semicore onset energy (M-edge) of
these materials.Comment: To appear in Phys. Rev.

### Energy loss of charged particles moving parallel to a magnesium surface

We present it ab initio calculations of the electronic energy loss of charged
particles moving outside a magnesium surface, from a realistic description of
the one-electron band structure and a full treatment of the dynamical
electronic response of valence electrons. Our results indicate that the finite
width of the plasmon resonance, which is mainly due to the presence of
band-structure effects, strongly modifies the asymptotic behaviour of the
energy loss at large distances from the surface. This effect is relevant for
the understanding of the interaction between charged particles and the internal
surface of microcapillaries.Comment: 7 pages, 3 figures. To appear in Phys. Rev.

### Noncovalent Interactions by QMC: Speedup by One-Particle Basis-Set Size Reduction

While it is empirically accepted that the fixed-node diffusion Monte-Carlo
(FN-DMC) depends only weakly on the size of the one-particle basis sets used to
expand its guiding functions, limits of this observation are not settled yet.
Our recent work indicates that under the FN error cancellation conditions,
augmented triple zeta basis sets are sufficient to achieve a benchmark level of
0.1 kcal/mol in a number of small noncovalent complexes. Here we report on a
possibility of truncation of the one-particle basis sets used in FN-DMC guiding
functions that has no visible effect on the accuracy of the production FN-DMC
energy differences. The proposed scheme leads to no significant increase in the
local energy variance, indicating that the total CPU cost of large-scale
benchmark noncovalent interaction energy FN-DMC calculations may be reduced.Comment: ACS book chapter, accepte

### Structural, Vibrational, and Electronic Study of α‑As2Te3 under Compression

This document is the Accepted Manuscript version of a Published Work that appeared in final form in
Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher.
To access the final edited and published work see http://dx.doi.org/10.1021/acs.jpcc.6b06049We report a study of the structural, vibrational, and electronic
properties of layered monoclinic arsenic telluride (α-As2Te3) at high
pressures. Powder X-ray diffraction and Raman scattering measurements up
to 17 GPa have been complemented with ab initio total-energy, lattice
dynamics, and electronic band structure calculations. Our measurements,
which include previously unreported Raman scattering measurements for
crystalline α-As2Te3, show that this compound undergoes a reversible phase
transition above 14 GPa at room temperature. The monoclinic crystalline
structure of α-As2Te3 and its behavior under compression are analyzed by
means of the compressibility tensor. Major structural and vibrational changes
are observed in the range between 2 and 4 GPa and can be ascribed to the
strengthening of interlayer bonds. No evidence of any isostructural phase
transition has been observed in α-As2Te3. A comparison with other group 15
sesquichalcogenides allows understanding the structure of α-As2Te3 and its
behavior under compression based on the activity of the cation lone electron pair in these compounds. Finally, our electronic
band structure calculations show that α-As2Te3 is a semiconductor at 1 atm, which undergoes a trivial semiconducting−metal
transition above 4 GPa. The absence of a pressure-induced electronic topological transition in α-As2Te3 is discussed.This work has been performed under financial support from Projects MAT2013-46649-C4-2-P, MAT2013-46649-C4-3-P, MAT2015-71070-REDC, FIS2013-48286-C2-1-P, and FIS2013-48286-C2-2-P of the Spanish Ministry of Economy and Competitiveness (MINECO), and the Department of Education, Universities and Research of the Basque Government and UPV/EHU (Grant No. IT756-13). This publication is also fruit of "Programa de Valoracion y Recursos Conjuntos de I+D+i VLC/CAMPUS" and has been financed by the Spanish Ministerio de Educacion, Cultura y Deporte as part of "Programa Campus de Excelencia Internacional" through Projects SP20140701 and SP20140871. Finally, authors thank ALBA Light Source for beam allocation at beamline MSPD.Cuenca Gotor, VP.; Sans-Tresserras, JÁ.; Ibáñez, J.; Popescu, C.; Gomis, O.; Vilaplana Cerda, RI.; Manjón Herrera, FJ.... (2016). Structural, Vibrational, and Electronic Study of α‑As2Te3 under Compression. Journal of Physical Chemistry C. 120(34):19340-19352. https://doi.org/10.1021/acs.jpcc.6b06049S19340193521203