131 research outputs found
Electronic, dielectric and optical properties of two dimensional and bulk ice: a multi-scale simulation study
The intercalated water into nanopores exhibits anomalous properties such as
ultralow dielectric constant.~Multi-scale modeling and simulations are used to
investigate the dielectric properties of various crystalline two-dimensional
ices and bulk ices. Although, the structural properties of two-dimensional
(2D-) ices have been extensively studied, much less is known about their
electronic and optical properties. First, by using density functional theory
(DFT) and density functional perturbation theory (DFPT), we calculate the key
electronic, optical and dielectric properties of 2D-ices. Performing DFPT
calculations, both the ionic and electronic contributions of the dielectric
constant are computed. The in-plane electronic dielectric constant is found to
be larger than the out-of-plane dielectric constant for all the studied
2D-ices. The in-plane dielectric constant of the electronic response is found
to be isotropic for all the studied ices. Secondly, we determined the dipolar
dielectric constant of 2D-ices using molecular dynamics simulations (MDS) at
finite temperature. The total out-of-plane dielectric constant is found to be
larger than 2 for all the studied 2D-ices. Within the framework of the
random-phase approximation (RPA), the absorption energy ranges for 2D-ices are
found to be in the ultraviolet spectra. For the comparison purposes, we also
elucidate the electronic, dielectric and optical properties of four crystalline
ices (ice VIII, ice XI, ice Ic and ice Ih) and bulk water
Tight-Binding Studio: A Technical Software Package to Find the Parameters of Tight-Binding Hamiltonian
We present the Tight-Binding Studio (TBStudio) software package for
calculating tight-binding Hamiltonian from a set of Bloch energy bands obtained
from first principle theories such as density functional theory, Hartree-Fock
calculations or Semi-empirical band structure theory. This will be helpful for
scientists who are interested in studying the electronic properties of
structures using Green's function theory in tight-binding approximation.
TBStudio is a cross-platform application written in C++ with a graphical user
interface design that is user-friendly and easy to work with. This software is
powered by Linear Algebra Package C interface library for solving the
eigenvalue problems and the standard high-performance OpenGL graphic library
for real-time plotting. TBStudio and its examples together with the tutorials
are available for download from tight-binding.com
The Pragmatic Instruction Effects on Persian EFL Learnersâ Noticing and Learning Outcomes in Request Forms
This study investigates the request strategies used by Persian learners of English as a Foreign Language (EFL), aimed at exploring the pragmatic instruction effects on their noticing constrained by different types of treatment tasks. The subsequent effect of the learnersâ noticing on their learning outcomes is taken into account as well. Thirty learners were divided into two instructional (treatment) conditions: a form-comparison condition and a form-search condition. Discourse completion tests were used to generate data related to the request strategies used by each group in pre- and posttests. The treatment data were examined regarding the extent to which the learners had noticed the appropriate manner of request realization in English and were further compared with the posttest. The findings revealed that during the treatment, the amount of learnersâ noticing the target request forms in the form-comparison condition was greater than the form-search condition. Furthermore, learnersâ higher awareness of the target request forms in the form-comparison condition could lead them to have a better performance in their posttest
The properties of electron transport through CNT/trans-PA/CNT system
Abstract Using a tight-binding model and a tranfer-matrix technique, we numerically investigate the effects of the coupling strength, and the length of the molecule on the electronic transmission through a CNT/(single) molecule/CNT system. With trans-polyacetylene (trans-PA) as the molecule sandwiched between two semi-infinite carbon nanotube(CNT), we rely on Landauer formalism as the basis for studying the conductance properties of this system. Our calculations show that the conductance is sensitive to the CNT/molecule coupling and that it exponentially decreases with the increase in the length of the molecule, as expected
- âĻ