22 research outputs found
A THz-Vibration to THz-Radiation Converter Based on Gold Nanoobjects: a Feasibility Study
The estimations done confirm a feasibility of the idea that gold nanobars
(GNBs) and nanorings (GNRs) irradiated by microwaves could become the terahertz
(THz) emitters with photon energies within the full width at half maximum of
longitudinal acoustic phononic DOS of gold (~13.7-17.5 meV, i.e., 3.3-4.2 THz).
A scheme of the THz radiation source is suggested based on the domestic
microwave oven irradiating a substrate with multiple deposited GNBs or GNRs.Comment: 5 pages, 3 figure
First-principles study of hydrogen dynamics in monoclinic TiO
The existence of intrinsic vacancies in cubic (monoclinic) TiO suggests
opportunity for hydrogen absorption, which was addressed in recent experiments.
In the present work, based on first principle calculations, the preferences are
studied for the hydrogen absorption sites and diffusion paths between them. The
oxygen vacancies are found to be primary hydrogen traps with absorption energy
of -2.87 eV. The plausible channels for hydrogen diffusion between adjacent
vacancy sites (ordered in the monoclinic TiO structure) are compared with the
help of calculations done with the nudge elastic band method. Several
competitive channels are identified, with barrier heights varying from 2.87 to
3.71 eV, that is high enough to ensure relative stability of trapped hydrogen
atoms at oxygen vacancy sites. Moreover, the possibility of adsorption of
molecular hydrogen was tested and found improbable, in the sense that the H2
molecules penetrating the TiO crystal are easily dissociated (and released
atoms tend to proceed towards oxygen vacancy sites). These results suggest that
hydrogen may persist in oxygen vacancy sites up to high enough temperatures.Comment: updated and enlarged version, accepted for publication in Journal of
Physical Chemistry C (June 2023
Calculation of the ground-state Stark effect in small molecules using the variational quantum eigensolver
As quantum computing approaches its first commercial implementations, quantum
simulation emerges as a potentially ground-breaking technology for several
domains, including Biology and Chemistry. However, taking advantage of quantum
algorithms in Quantum Chemistry raises a number of theoretical and practical
challenges at different levels, from the conception to its actual execution. We
go through such challenges in a case study of a quantum simulation for the
hydrogen (H2) and lithium hydride (LiH) molecules, at an actual commercially
available quantum computer, the IBM Q. The former molecule has always been a
playground for testing approximate calculation methods in Quantum Chemistry,
while the latter is just a little bit more complex, lacking the mirror symmetry
of the former. Using the Variational Quantum Eigensolver (VQE) method, we study
the molecule's ground state energy versus interatomic distance, under the
action of stationary electric fields (Stark effect). Additionally, we review
the necessary calculations of the matrix elements of the second quantization
Hamiltonian encompassing the extra terms concerning the action of electric
fields, using STO-LG type atomic orbitals to build the minimal basis sets.Comment: Soft Comput (2021
Magnetic properties of small Pt-capped Fe, Co and Ni clusters: A density functional theory study
Theoretical studies on M (M = Fe, Co, Ni) and MPt (for
= 3, 4, 5, 20) clusters including the spin-orbit coupling are done using
density functional theory. The magnetic anisotropy energy (MAE) along with the
spin and orbital moments are calculated for M icosahedral clusters. The
angle-dependent energy differences are modelled using an extended classical
Heisenberg model with local anisotropies. From our studies, the MAE for
Jahn-Teller distorted Fe, Mackay distorted Fe and nearly
undistorted Co clusters are found to be 322, 60 and 5 eV/atom,
respectively, and are large relative to the corresponding bulk values, (which
are 1.4 and 1.3 eV/atom for bcc Fe and fcc Co, respectively.) However, for
Ni (which practically does not show relaxation tendencies), the
calculated value of MAE is found to be 0.64 eV/atom, which is
approximately four times smaller compared to the bulk fcc Ni (2.7
eV/atom). In addition, MAE of the capped cluster (FePt) is
enhanced compared to the uncapped Jahn-Teller distorted Fe cluster
Terahertz-to-infrared converters for imaging the human skin cancer: challenges and feasibility
PURPOSE: Terahertz (THz) medical imaging is a promising noninvasive technique for monitoring the skin's conditions, early detection of the human skin cancer, and recovery from burns and wounds. It can be applied for visualization of the healing process directly through clinical dressings and restorative ointments, minimizing the frequency of dressing changes. The THz imaging technique is cost effective, as compared to the magnetic resonance method. Our aim was to develop an approach capable of providing better image resolution than the commercially available THz imaging cameras. APPROACH: The terahertz-to-infrared (THz-to-IR) converters can visualize the human skin cancer by converting the latter's specific contrast patterns recognizable in THz radiation range into IR patterns, detectable by a standard IR imaging camera. At the core of suggested THz-to-IR converters are flat matrices transparent both in the THz range to be visualized and in the operating range of the IR camera, these matrices contain embedded metal nanoparticles (NPs), which, when irradiated with THz rays, convert the energy of THz photons into heat and become nanosources of IR radiation detectable by an IR camera. RESULTS: The ways of creating the simplest converter, as well as a more complex converter with wider capabilities, are considered. The first converter is a gelatin matrix with gold 8.5-nm diameter NPs, and the second is a polystyrene matrix with 2-nm diameter NPs from copper-nickel MONEL ® alloy 404. CONCLUSIONS: An approach with a THz-to-IR converter equipped with an IR camera is promising in that it could provide a better image of oncological pathology than the commercially available THz imaging cameras do
Siesta: Recent developments and applications
A review of the present status, recent enhancements, and applicability of the Siesta program is presented. Since its debut in the mid-1990s, Siesta?s flexibility, efficiency, and free distribution have given advanced materials simulation capabilities to many groups worldwide. The core methodological scheme of Siesta combines finite-support pseudo-atomic orbitals as basis sets, norm-conserving pseudopotentials, and a real-space grid for the representation of charge density and potentials and the computation of their associated matrix elements. Here, we describe the more recent implementations on top of that core scheme, which include full spin?orbit interaction, non-repeated and multiple-contact ballistic electron transport, density functional theory (DFT)+U and hybrid functionals, time-dependent DFT, novel reduced-scaling solvers, density-functional perturbation theory, efficient van der Waals non-local density functionals, and enhanced molecular-dynamics options. In addition, a substantial effort has been made in enhancing interoperability and interfacing with other codes and utilities, such as wannier90 and the second-principles modeling it can be used for, an AiiDA plugin for workflow automatization, interface to Lua for steering Siesta runs, and various post-processing utilities. Siesta has also been engaged in the Electronic Structure Library effort from its inception, which has allowed the sharing of various low-level libraries, as well as data standards and support for them, particularly the PSeudopotential Markup Language definition and library for transferable pseudopotentials, and the interface to the ELectronic Structure Infrastructure library of solvers. Code sharing is made easier by the new open-source licensing model of the program. This review also presents examples of application of the capabilities of the code, as well as a view of on-going and future developments.SIESTA development was historically supported by different Spanish National Plan projects (Project Nos. MEC-DGES-PB95-0202, MCyT-BFM2000-1312, MEC-BFM2003-03372, FIS2006-12117, FIS2009-12721, FIS2012-37549, FIS2015-64886-P, and RTC-2016-5681-7), the latter one together with Simune Atomistics Ltd. We are thankful for financial support from the Spanish Ministry of Science, Innovation and Universities through Grant No. PGC2018-096955-
Siesta: Recent developments and applications
A review of the present status, recent enhancements, and applicability of the SIESTA program is presented. Since its debut in the mid-1990s,
SIESTA’s flexibility, efficiency, and free distribution have given advanced materials simulation capabilities to many groups worldwide. The core
methodological scheme of SIESTA combines finite-support pseudo-atomic orbitals as basis sets, norm-conserving pseudopotentials, and a realspace grid for the representation of charge density and potentials and the computation of their associated matrix elements. Here, we describe
the more recent implementations on top of that core scheme, which include full spin–orbit interaction, non-repeated and multiple-contact
ballistic electron transport, density functional theory (DFT)+U and hybrid functionals, time-dependent DFT, novel reduced-scaling solvers,
density-functional perturbation theory, efficient van der Waals non-local density functionals, and enhanced molecular-dynamics options. In
addition, a substantial effort has been made in enhancing interoperability and interfacing with other codes and utilities, such as WANNIER90 and
the second-principles modeling it can be used for, an AiiDA plugin for workflow automatization, interface to Lua for steering SIESTA runs, and
various post-processing utilities. SIESTA has also been engaged in the Electronic Structure Library effort from its inception, which has allowed
the sharing of various low-level libraries, as well as data standards and support for them, particularly the PSeudopotential Markup Language
definition and library for transferable pseudopotentials, and the interface to the ELectronic Structure Infrastructure library of solvers. Code
sharing is made easier by the new open-source licensing model of the program. This review also presents examples of application of the
capabilities of the code, as well as a view of on-going and future developments.
Published under license by AIP Publishing.Siesta development was historically supported by different Spanish National Plan projects (Project Nos. MEC-DGES-PB95-0202, MCyT-BFM2000-1312, MEC-BFM2003-03372, FIS2006-12117, FIS2009-12721, FIS2012-37549, FIS2015-64886-P, and RTC-2016-5681-7), the latter one together with Simune Atomistics Ltd. We are thankful for financial support from the Spanish Ministry of Science, Innovation and Universities through Grant No. PGC2018-096955-B.
We acknowledge the Severo Ochoa Center of Excellence Program [Grant Nos. SEV-2015-0496 (ICMAB) and SEV-2017-0706 (ICN2)], the GenCat (Grant No. 2017SGR1506), and the European Union MaX Center of Excellence (EU-H2020 Grant No. 824143).
P.G.-F. acknowledges support from Ramón y Cajal (Grant No. RyC-2013-12515). J.I.C. acknowledges Grant No. RTI2018-097895-B-C41.
R.C. acknowledges the European Union’s Horizon 2020 Research and Innovation Program under Marie Skłodoswka-Curie Grant Agreement No. 665919.
D.S.P, P.K., and P.B. acknowledge Grant No. MAT2016-78293-C6, FET-Open No. 863098, and UPV-EHU Grant No. IT1246-19.
V. W. Yu was supported by a MolSSI Fellowship (U.S. NSF Award No. 1547580), and V.B. and V.W.Y. were supported by the ELSI Development by the NSF (Award No. 1450280). We also acknowledge Honghui Shang and Xinming Qin for giving us access to the honpas code, where a preliminary version of the hybrid functional support described here was implemented.
We are indebted to other contributors to the Siesta project whose names can be seen in the Docs/Contributors.txt file of the Siesta distribution, and we thank those, too many to list, contributing fixes, comments, clarifications, and documentation for the code.Peer reviewe