47 research outputs found
Revealing the formation and electrochemical properties of bis(trifluoromethanesulfonyl) imide intercalated graphite with first-principles calculations
Graphite has been reported to have anion as well as cation intercalation
capacities as both cathode and anode host materials for the dual ion battery.
In this work, we study the intercalation of bis(trifluoromethanesulfonyl) imide
(TFSI) anion from ionic liquid electrolyte into graphite with first-principles
calculations. We build models for TFSI-C compounds with systematically
increasing unit cell sizes of graphene sheet and investigate their stabilities
by calculating the formation energy, resulting in the linear decrease and
arriving at the limit of stability. With identified unit cell sizes for stable
compound formation, we reveal that the interlayer distance and relative volume
expansion ratio of TFSI-C increase as increasing the concentration of TFSI
intercalate during the charge process. The electrode voltage is determined to
be ranged from 3.8 V to 3.0 V at the specific capacity ranging from 30 mAh
g to 54 mAh g in agreement with experiment. Moreover, a very low
activation barrier of under 50 meV for TFSI migration and good electronic
conductivity give a proof of using these compounds as a promising cathode.
Through the analysis of charge transfer, we clarify the mechanism of TFSI-C
formation, and reveal new prospects for developing graphite based cathode
Influence of halide composition on the structural, electronic, and optical properties of mixed CHNHPb(IBr) perovskites calculated using the virtual crystal approximation method
We investigate the structural, electronic and optical properties of mixed
bromide-iodide lead perovskite solar cell CHNHPb(IBr)
by means of the virtual crystal approximation (VCA) within density functional
theory (DFT). Optimizing the atomic positions and lattice parameters increasing
the bromide content from 0.0 to 1.0, we fit the calculated lattice
parameter and energy band gap to the linear and quadratic function of Br
content, respectively, which are in good agreement with the experiment,
respecting the Vegard's law. With the calculated exciton binding energy and
light absorption coefficient, we make sure that VCA gives consistent results
with the experiment, and the mixed halide perovskites are suitable for
generating the charge carriers by light absorption and conducting the carriers
easily due to their strong photon absorption coefficient, low exciton bindign
energy, and high carrier mobility at low Br contents. Furthermore analyzing the
bonding lengths between Pb and X (IBr: virtual atom) as well as C
and N, we stress that the stability of perovskite solar cell is definitely
improved at =0.2
First-principles study on the electronic and optical properties of inorganic perovskite Rb1-xCsxPbI3 for solar cell applications
Recently, replacing or mixing organic molecules in the hybrid halide
perovskites with the inorganic Cs or Rb cations has been reported to increase
the material stability with the comparable solar cell performance. In this
work, we systematically investigate the electronic and optical properties of
all-inorganic alkali iodide perovskites Rb1-xCsxPbI3 using the first-principles
virtual crystal approximation calculations. Our calculations show that as
increasing the Cs content x, lattice constants, band gaps, exciton binding
energies, and effective masses of charge carriers decrease following the
quadratic (linear for effective masses) functions, while static dielectric
constants increase following the quadratic function, indicating an enhancement
of solar cell performance upon the Rb addition to CsPbI3. When including the
many-body interaction within the GW approximation and incorporating the
spin-orbit coupling (SOC), we obtain more reliable band gap compared with
experiment for CsPbI3, highlighting the importance of using GW+SOC approach for
the all-inorganic as well as organic-inorganic hybrid halide perovskite
materials
Reductive property of new fuzzy reasoning method based on distance measure
Firstly in this paper we propose a new criterion function for evaluation of
the reductive property about the fuzzy reasoning result for fuzzy modus ponens
and fuzzy modus tollens. Secondly unlike fuzzy reasoning methods based on the
similarity measure, we propose a new fuzzy reasoning method based on distance
measure. Thirdly the reductive property for 5 fuzzy reasoning methods are
checked with respect to fuzzy modus ponens and fuzzy modus tollens. Through the
experiment, we show that proposed method is better than the previous methods in
accordance with human thinking
Formation and characterization of ceramic coating from alumino silicate mineral powders in the matrix of cement composite on the concrete wall
Enhancement of thermal performance of concrete wall is nowadays of great
importance in reducing the operational energy demand of buildings. We developed
a new kind of inorganic coating material based on \ce{SiO2}-\ce{Al2O3}-rich
minerals and Portland cement (PC) powder. The finely pulverized mineral powder
with the particle size distribution (PSD) of 0.4-40 m was mixed with the
vehicle solvent containing some agents, cement powder with PSD of 2-100 m,
and water in the certain weight ratio, producing the colloid solution. After
application within 2 hours to the plaster layer of concrete wall and sufficient
long hardening period of over three months, the coating layer of 0.6-1.0 mm
thickness was observed to become a densified ceramic. Powder X-ray diffraction
(XRD) experiments were performed to identify the crystalline components of
minerals, cement and ceramic coating powders. Three- and two-dimensional
surface morphologies and chemical compositions of coating material were
obtained with the optical interferometer and scanning electron microscope (SEM)
equipped with an energy dispersive X-ray analyzer (EDX). These XRD and SEM/EDX
analyses demonstrated obviously that the coating layer is mainly composed of
the calcium-silicate-hydrate (C-S-H) and the calcium-aluminate-hydrate (C-A-H)
ceramics with the relatively small number of closed pores (10\% porosity)
compared with the cement mortar and concrete layers. Two-step hydrations of
cement and subsequently \ce{SiO2}-\ce{Al2O3} promoted by the alkali product
\ce{Ca(OH)2} were proposed as the main mechanism of ceramic formation
First-principles study on the chemical decomposition of inorganic perovskites \ce{CsPbI3} and \ce{RbPbI3} at finite temperature and pressure
Inorganic halide perovskite \ce{Cs(Rb)PbI3} has attracted significant
research interest in the application of light-absorbing material of perovskite
solar cells (PSCs). Although there have been extensive studies on structural
and electronic properties of inorganic halide perovskites, the investigation on
their thermodynamic stability is lack. Thus, we investigate the effect of
substituting Rb for Cs in \ce{CsPbI3} on the chemical decomposition and
thermodynamic stability using first-principles thermodynamics. By calculating
the formation energies of solid solutions \ce{CsRbPbI3} from their
ingredients \ce{CsRbI} and \ce{PbI2}, we find that the best match
between efficiency and stability can be achieved at the Rb content
0.7. The calculated Helmholtz free energy of solid solutions indicates that
\ce{CsRbPbI3} has a good thermodynamic stability at room
temperature due to a good miscibility of \ce{CsPbI3} and \ce{RbPbI3}. Through
lattice-dynamics calculations, we further highlight that \ce{RbPbI3} never
stabilize in cubic phase at any temperature and pressure due to the chemical
decomposition into its ingredients \ce{RbI} and \ce{PbI2}, while \ce{CsPbI3}
can be stabilized in the cubic phase at the temperature range of 0600 K and
the pressure range of 04 GPa. Our work reasonably explains the experimental
observations, and paves the way for understanding material stability of the
inorganic halide perovskites and designing efficient inorganic halide PSCs
Ab initio investigation of the adsorption of zoledronic acid molecule on hydroxyapatite (001) surface: an atomistic insight of bone protection
We report a computational study of the adsorption of zoledronic acid molecule
on hydroxyapatite (001) surface within ab initio density functional theory. The
systematic study has been performed, from hydroxyapatite bulk and surface, and
zoledronic acid molecule to the adsorption of the molecule on the surface. The
optimized bond lengths and bond angles were obtained and analyzed, giving an
evidence of structural similarity between subjects under study. The formation
energies of hydroxyapatite (001) surfaces with two kinds of terminations were
computed as about 1.2 and 1.5 J/m^2 with detailed atomistic structural
information. We determined the adsorption energies of zoledronic acid molecule
on the surfaces, which are -260 kJ/mol at 0.25 ML and -400 kJ/mol at 0.5 ML. An
atomistic insight of strong binding affinity of zoledronic acid to the
hydroxyapatite surface was given and discussed.Comment: 11 pages, 8 figure
Ab initio Investigation of Adsorption Characteristics of Bisphosphonates on Hydroxyapatite (001) Surface
The structures of some bisphosphonates (clodronate, etidronate, pamidronate,
alendronate, risedronate, zoledronate, minodronate) were obtained and analyzed,
and their adsorption energies onto hydroxyapatite (001) surface were compared
to find out ranking order of binding affinity, which shows that the adsorption
energy is the largest for pamidronate, followed by alendronate, zoledronate,
clodronate, ibandronate, the lowest for minodronate and etidronate
First-principles study of ternary graphite compounds cointercalated with alkali atoms (Li, Na, and K) and alkylamines towards alkali ion battery applications
Using density functional theory calculations, we have investigated the
structural, energetic, and electronic properties of ternary graphite
intercalation compounds (GICs) containing alkali atoms (AM) and normal
alkylamine molecules (nC), denoted as AM-nC-GICs (AM=Li, Na, K, =1, 2,
3, 4). The orthorhombic unit cells have been used to build the models for
crystalline stage-I AM-nC-GICs. By performing the variable cell relaxations
and the analysis of results, we have found that with the increase in the atomic
number of alkali atoms the layer separations decreases in contrast to AM-GICs,
while the bond lengths of alkali atoms with graphene layer and nitrogen atom of
alkylamine decreases. The formation and interlayer binding energies of
AM-nC3-GICs have been calculated, indicating the increase in stability from Li
to K. The calculated energy barriers for migration of alkali atoms suggest that
alkali cation with larger ionic radius diffuses in graphite more smoothly,
being similar to AM-GICs. The analysis of density of states, electronic density
differences, and atomic populations illustrates a mechanism how the insertion
of especially Na among alkali atoms into graphite with first stage can be made
easy by cointercalation with alkylamine, more extent of electronic charge
transfer is occurred from more electropositive alkali atom to carbon ring of
graphene layer, while alkylamine molecules interact strongly with graphene
layer through the hybridization of valence electron orbitals.Comment: 22 pages, 9 figure
A Security Protocol for the Identification and Data Encrypt Key Management of Secure Mobile Devices
In this paper, we proposed an identification and data encrypt key manage
protocol that can be used in some security system based on such secure devices
as secure USB memories or RFIDs, which are widely used for identifying persons
or other objects recently. In general, the default functions of the security
system using a mobile device are the authentication for the owner of the device
and secure storage of data stored on the device. We proposed a security model
that consists of the server and mobile devices in order to realize these
security features. In this model we defined the secure communication protocol
for the authentication and management of data encryption keys using a private
key encryption algorithm with the public key between the server and mobile
devices. In addition, we was performed the analysis for the attack to the
communication protocol between the mobile device and server. Using the
communication protocol, the system will attempt to authenticate the mobile
device. The data decrypt key is transmitted only if the authentication process
is successful. The data in the mobile device can be decrypted using the key.
Our analysis proved that this Protocol ensures anonymity, prevents replay
attacks and realizes the interactive identification between the security
devices and the authentication server.Comment: 7 pages, 1 figure, in version 2 added a secure cryptographic key
management protocol based on the secure user authentication scheme in version
1 and references, changed the title; version 3 developed abstract and
conclusions, accepted in JTP