81 research outputs found
First principles electron-correlated calculations of optical absorption in magnesium clusters
In this paper, we report large-scale configuration interaction (CI)
calculations of linear optical absorption spectra of various isomers of
magnesium clusters Mg (n=2--5), corresponding to valence transitions.
Geometry optimization of several low-lying isomers of each cluster was carried
out using coupled-cluster singles doubles (CCSD) approach, and these geometries
were subsequently employed to perform ground and excited state calculations
using either the full-CI (FCI) or the multi-reference singles-doubles
configuration interaction (MRSDCI) approach, within the frozen-core
approximation. Our calculated photoabsorption spectrum of magnesium dimer
(Mg) isomer is in excellent agreement with the experiments both for peak
positions, and intensities. Owing to the sufficiently inclusive
electron-correlation effects, these results can serve as benchmarks against
which future experiments, as well as calculations performed using other
theoretical approaches, can be tested.Comment: 23 pages and 21 figures of main tex
Optical Absorption in B Cluster: A Time-Dependent Density Functional Approach
The linear optical absorption spectra of three isomers of planar boron
cluster B are calculated using time-dependent spin-polarized density
functional approach. The geometries of these cluster are optimized at the
B3LYP/6-311+G* level of theory. Even though the isomers are almost degenerate,
the calculated spectra are quite different, indicating a strong
structure-property relationship. Therefore, these computed spectra can be used
in the photo-absorption experiments to distinguish between different isomers of
a cluster.Comment: Version2: Latex and hyperref enabled. Minor typos corrected. 4
figures, 2 pages. Accepted manuscript. To appear in AIP Conference
Proceeding
Remarkable Hydrogen Storage on Beryllium Oxide Clusters: First Principles Calculations
Since the current transportation sector is the largest consumer of oil, and
subsequently responsible for major air pollutants, it is inevitable to use
alternative renewable sources of energies for vehicular applications. The
hydrogen energy seems to be a promising candidate. To explore the possibility
of achieving a solid-state high-capacity storage of hydrogen for onboard
applications, we have performed first principles density functional theoretical
calculations of hydrogen storage properties of beryllium oxide clusters
(BeO) (n=2 -- 8). We observed that polar BeO bond is responsible for
H adsorption. The problem of cohesion of beryllium atoms does not arise,
as they are an integral part of BeO clusters. The (BeO) (n=2 -- 8)
adsorbs 8--12 H molecules with an adsorption energy in the desirable
range of reversible hydrogen storage. The gravimetric density of H
adsorbed on BeO clusters meets the ultimate 7.5 wt% limit, recommended for
onboard practical applications.
In conclusion, beryllium oxide clusters exhibit a remarkable solid-state
hydrogen storage.Comment: This document is the Accepted Manuscript version of a Published Work
that appeared in final form in JPCC, copyright American Chemical Society
after peer review and technical editing by the publisher. To access the final
edited and published work see , see
http://pubs.acs.org/doi/abs/10.1021/jp410994
Large-scale first principles configuration interaction calculations of optical absorption in boron clusters
We have performed systematic large-scale all-electron correlated calculations
on boron clusters B(n=2--5), to study their linear optical absorption
spectra. Several possible isomers of each cluster were considered, and their
geometries were optimized at the coupled-cluster singles doubles (CCSD) level
of theory. Using the optimized ground-state geometries, excited states of
different clusters were computed using the multi-reference singles-doubles
configuration-interaction (MRSDCI) approach, which includes electron
correlation effects at a sophisticated level. These CI wave functions were used
to compute the transition dipole matrix elements connecting the ground and
various excited states of different clusters, eventually leading to their
linear absorption spectra. The convergence of our results with respect to the
basis sets, and the size of the CI expansion were carefully examined. The
contribution of configurations to many body wavefunction of various excited
states suggests that the excitations involved are collective, plasmonic type.Comment: 25 page, 13 figures (included); Invited article for a special issue
titled "Theoretical Simulation and Computational Design of Nanomaterials and
Biomaterials", of the journal Nano Lif
Pressure-Induced Topological Phase Transitions in CdGeSb and CdSnSb
Topological quantum phase transitions (TQPTs) in a material induced by
external perturbations are often characterized by band touching points in the
Brillouin zone. The low-energy excitations near the degenerate band touching
points host different types of fermions while preserving the topological
protection of surface states. An interplay of different tunable topological
phases offers an insight into the evolution of the topological character. In
this paper, we study the occurrence of TQPTs as a function of hydrostatic
pressure in CdGeSb and CdSnSb chalcopyrites, using the first-principles
calculations. At ambient pressure, both materials are topological insulators
having a finite band gap with inverted order of Sb- and Sb-,
orbitals of valence bands at the point. On the application of
hydrostatic pressure the band gap reduces, and at the critical point of the
phase transition, these materials turn into Dirac semimetals. On further
increasing the pressure beyond the critical point, the band inversion is
reverted making them trivial insulators. The pressure-induced change in band
topology from non-trivial to trivial phase is also captured by L\"{u}ttinger
model Hamiltonian calculations. Our model demonstrates the critical role played
by a pressure-induced anisotropy in frontier bands in driving the phase
transitions. These theoretical findings of peculiar coexistence of multiple
topological phases in the same material provide a realistic and promising
platform for the experimental realization of the TQPT.Comment: 7 pages, 7 figure
Multiple Triple-Point Fermions in Heusler Compounds
Using the density functional theoretical calculations, we report a new set of
topological semimetals XYZ (X = \{Cu, Rh, Pd, Ag, Au, Hg\}, Y = \{Li, Na,
Sc, Zn, Y, Zr, Hf, La, Pr, Pm, Sm, Tb, Dy, Ho, Tm\} and Z =\{Mg, Al, Zn, Ga, Y,
Ag, Cd, In, Sn, Ta, Sm\}), which show the existence of multiple topological
triple point fermions along four independent axes. These fermionic
quasiparticles have no analogues elementary particle in the standard model. The
angle-resolved photoemission spectroscopy is simulated to obtain the exotic
topological surface states and the characteristic Fermi arcs. The inclusion of
spin-orbit coupling splits the triple-point into two Dirac points. The
triple-point fermions are exhibited on the easily cleavable (111) surface and
are well separated from the surface point, allowing them to be
resolved in the surface spectroscopic techniques. This intermediate linearly
dispersive degeneracy between Weyl and Dirac points may offer prospective
candidates for quantum transport applications
Pattern of antibiotic use in neonatal intensive care unit in tertiary care hospital in Southern India
Background: Repeated and prolonged courses of antibiotics exposure have resulted in an increase in the prevalence of hospital acquired infections and antibiotic resistant profile. The objective of this study was to quantify the use of antibiotics in a neonatal intensive care unit (NICU) from rural tertiary health care centre.Methods: A hospital based cross-sectional study was conducted in the NICU of tertiary care hospital located in western Maharashtra, India during the year 2011-12. A total of 237 neonates admitted to NICU from October 2011 to March 2012 were enrolled in the study according to inclusion criteria of the study. Demographic details, data on antibiotic prescriptions (name, dose, frequency, route of administration) were recorded by utilizing pre-tested structured proforma.Results: A total of 3822 prescriptions were received by the neonates and commonly prescribed antibiotics were amikacin (75.53%), cefotaxime (43.34%) and ampicillin (31.33%) respectively. It was also noted that 50% of the drugs prescribed were in compliance with the national list of essential medicines 2011. The max, 68.75% of antibiotics prescribed were in generics forms however, 12.5% were prescribed in the form of fixed dose combinations.Conclusions: The revealed that 3rd generation cephalosporins and amikacin are most commonly used antibiotics in NICU
Soft-Dropout: A Practical Approach for Mitigating Overfitting in Quantum Convolutional Neural Networks
Quantum convolutional neural network (QCNN), an early application for quantum
computers in the NISQ era, has been consistently proven successful as a machine
learning (ML) algorithm for several tasks with significant accuracy. Derived
from its classical counterpart, QCNN is prone to overfitting. Overfitting is a
typical shortcoming of ML models that are trained too closely to the availed
training dataset and perform relatively poorly on unseen datasets for a similar
problem. In this work we study the adaptation of one of the most successful
overfitting mitigation method, knows as the (post-training) dropout method, to
the quantum setting. We find that a straightforward implementation of this
method in the quantum setting leads to a significant and undesirable
consequence: a substantial decrease in success probability of the QCNN. We
argue that this effect exposes the crucial role of entanglement in QCNNs and
the vulnerability of QCNNs to entanglement loss. To handle overfitting, we
proposed a softer version of the dropout method. We find that the proposed
method allows us to handle successfully overfitting in the test cases.Comment: 9 pages, 14 images, 6 table
Dielectric relaxation of 1-nitropropane-ethanol mixtures using pico second time domain technique from 10 MHz to 50 GHz
Complex dielectric measurements in the frequency range 10 MHz - 50 GHz have been carried out in 1-nitropropane-ethanol mixtures with various concentrations by using a time domain reflectometry (TDR) at 283 K to 298 K. The dielectric relaxation response of 1-nitropropane-ethanol mixtures have been analyzed by using Debye model. The dielectric parameters such as static dielectric constant, relaxation time, excess permittivity, excess inverse relaxation time, Kirkwood correlation factor, enthalpy of activation and Gibbs free energy of activation have been determined for 1-nitropropane-ethanol system. The study confirms that the intermolecular interaction varies significantly with the increase in concentration of 1-nitropropane in ethanol
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