First-principles Plane-wave Calculations Research Articles

Fragment Orbitals Extracted from First-Principles Plane-Wave Calculations.

Decomposing extended structures into smaller, molecular, even functional groups or simple fragments has a long tradition in chemistry because it allows for understanding certain electronic peculiarities in truly chemical terms. By doing so, invaluable property information is chemically accessible, for example, needed to rationalize catalytic or magnetic or optical nature. In order to also follow that train of thought for periodic materials, we have developed a tool which in a straightforward manner derives fragment molecular orbitals from plane-wave electronic-structure data of whatever kind of solid-state material. We here report on the mathematical apparatus of the method dubbed linear combination of fragment orbitals (LCFO) used for that purpose, implemented within the LOBSTER code. The method is illustrated from various sorts of molecular entities contained in such crystalline materials, together with an assessment of both accuracy and robustness of the new tool.

Exploring the potential of MnX (S, Sb) monolayers for antiferromagnetic spintronics: A theoretical investigation

In this study, we predicted new two-dimensional tetragonal structures of t-Mn2X2 (X = S, Sb) sheets on the basis of first-principles plane wave calculations within density functional theory with Hubbard U model. Stability tests such as phonon spectrum calculation and molecular dynamic simulations reveal that the 2D t-Mn2X2 structures are dynamically and thermally stable at least in room temperature. Our theoretical calculations have shown that t-Mn2X2 structures have two Raman active and seven infrared active modes. The t-Mn2Sb2 sheet exhibits metallic property, whereas t-Mn2S2 shows semiconducting property with a 0.68 eV indirect bandgap. Exploring of the favorable magnetic orientation calculations revealed that both 2D t-Mn2X2 structures prefer antiferromagnetic spin configuration. Estimated critical temperatures for the phase transition from antiferromagnetic spin order to paramagnetic case are 720 K and 545 K for t-Mn2S2 and t-Mn2Sb2, respectively. These relatively high Néel temperatures and their suitable electronic properties for many applications clearly qualify that the 2D t-Mn2X2 sheets can be a good candidate for room temperature antiferromagnetic device applications.

Li adsorption on monolayer and bilayer MoS2 as an ideal substrate for hydrogen storage**Project supported by the National Key Basic Research Program of China (Grant No. 2012CB932304), the National Natural Science Foundation of China (Grant No. 21763007), the Innovation Team Foundation of the Education Department of Guizhou Province, China (Grant No. [2014]35), and the Key Laboratory of Low Dimensional Condensed

Based on the first-principles plane wave calculations, we show that Li adsorbed on monolayer and bilayer MoS2 forming a uniform and stable coverage can serve as a high-capacity hydrogen storage medium, and Li-coated MoS2 can be recycled by operations at room temperature due to Li having strength binding, big separation and is stable against clustering. The full Li coverage MoS2 system (2*2 hexagonal MoS2 supercell) can reach up to eight H2 molecules on every side, corresponding to the gravimetric density of hydrogen storage up to 4.8 wt% and 2.5 wt% in monolayer and bilayer MoS2, respectively. The adsorption energies of hydrogen molecules are in the range of 0.10eV/H2–0.25 eV/H2, which are acceptable for reversible H2 adsorption/desorption near ambient temperature. In addition, compared with light metals decorated low dimension carbon-based materials, the sandwiched structure of MoS2 exhibits the greatly enhanced binding stability of Li atoms as well as slightly decreased Li-Li interaction and thus avoids the problem of metal clustering. It is interesting to note that the Li atom apart from the electrostatic interaction, acts as a bridge of hybridization between the S atoms of MoS2 and adsorbed H2 molecules. The encouraging results show that such light metals decorated with MoS2 have great potential in developing high performance hydrogen storage materials.

High piezoelectricity in the buckled V-structure monolayers of group III-V: An Ab initio calculation

Using first-principles plane-wave calculations in the framework of density functional theory, we calculated the coefficients of elasticity, piezoelectric strain and stress tensors for the buckled V-structure group III-V monolayer materials (GaP, GaAs, InP, InAs). We demonstrated that these compounds have four independent elastic coefficients (c11, c21, c22, c66) and three piezoelectric coefficients (d11, d12, d26). Our analysis shows that the InAs (d11 = 64.47 p.m./V) and the GaAs (d11 = 35.39 p.m./V) monolayers exhibit much stronger piezoelectricity than reported two-dimensional materials such as the h-BN and the MoS2 monolayers. These nanomaterials that have simultaneously piezoelectricity and semiconducting behavior are promising candidates for piezotronics and piezo-phototronics applications.

Platinum Adsorption and Diffusion on Two-Dimensional Gallium Nitride

In this study, we examined the adsorption and diffusion of platinum (Pt) adatom on two-dimensional hexagonal gallium nitride (h-GaN), by using first-principles plane-wave calculations. Two different levels of platinum coverage ratio (θ=1/8 and θ=1/32) were considered and the changes in the electronic structure for high-level platinum coverage ratio (θ=1/8) were examined. Low-level coverage ratio (θ=1/32) is used to calculate the diffusion barrier energy of Pt adatom on GaN monolayer. Our theoretical calculations have shown that Pt atom strongly binds on the top of nitrogen atoms in GaN monolayer and high energy is required for its diffusion. While GaN monolayer has 2.1 eV indirect band gap (Γ→K), this band gap reduces to 1.3 eV with Pt adsorption. These results may lead to further investigations on forming Pt nanoparticles or Pt coating on GaN sheet.

Effect of Sn-Doping on Behavior of Li-Intercalation in V2O5 Cathode Materials of Li-Ion Batteries: A Computational Perspective

We utilized first-principles plane-wave calculations to obtain insight into the role of Sn-doping on the behavior of Li intercalation in V2O5 cathode materials used in Li-ion batteries. Density fun...

Effect of structural phase transformations under pressure on electronic and optical properties of CuInS2

First-principles plane-wave calculations were employed to study the phase transitions, electronic and optical properties of chalcopyrite CuInS2 (CIS) under pressure, which is a promising semiconductor compound material for nonlinear optical, photovoltaic and bio-applications. From the variations of Gibbs free energy and volume with pressure, we confirmed an experimentally found phase transformation of CIS from tetragonal I4¯2d structure into the cubic Fm3¯m phase. It occurs at 7.9 GPa with a volume reduction of 15.6%, which are comparable with the experimental values of 9.5 GPa and 12%. A new possible phase transition of CIS from the cubic Fm3¯m structure to the orthorhombic Cmcm structure under higher pressure was predicted occurring at 49.6 GPa with a volume reduction about 0.64%. Using the more accurate HSE06 functional, we found that the growth rate of energy gap with pressure (dEg/dP) for the I4¯2d phase is about 24.8 meV/GPa, very close to the experimental value of 24 meV/GPa. The calculated electronic properties for Fm3¯m and Cmcm phases show that CIS is a metallic material under high pressure, rather than a semiconductor. The optical absorption spectra indicate that with the increase of pressure the absorption edge of CIS becomes smaller while the optical energy gap is larger.

Adsorption of alkali and alkaline earth metal atoms and dimers on monolayer germanium carbide

First-principles plane wave calculations have been performed to study the adsorption of alkali and alkaline earth metals on monolayer germanium carbide (GeC). We found that the favourable adsorption sites on GeC sheet for single alkali and alkaline earth adatoms are generally different from graphene or germanene. Among them, Mg, Na and their dimers have weakly bounded to GeC due to their closed valence electron shells, so they may have high mobility on GeC. Two different levels of adatom coverage ( and ) have been investigated and we concluded that different electronic structures and magnetic moments for both coverages owing to alkali and alkaline earth atoms have long range electrostatic interactions. Lithium atom prefers to adsorbed on hollow site similar to other group-IV monolayers and the adsorption results in metallisation of GeC instead of semiconducting behaviour. Na and K adsorption can induce 1 total magnetic moment on GeC structures and they have shown semiconductor property which may have potential use in spintronic devices. We also showed that alkali or alkaline earth metal atoms can form dimer on GeC sheet. Calculated adsorption energies suggest that clustering of alkali and alkaline earth atoms is energetically favourable. All dimer adsorbed GeC systems have nonmagnetic semiconductor property with varying band gaps from 0.391 to 1.311 eV which are very suitable values for various device applications.

Lattice structures and electronic properties of WZ-CuInS2/WZ-CdS interface from first-principles calculations**Project supported by the National Natural Science Foundation of China (Grant Nos. 11164014 and 11364025) and the Gansu Science and Technology Pillar Program, China (Grant No. 1204GKCA057).

Using the first-principles plane-wave calculations within density functional theory, the perfect bi-layer and monolayer terminated WZ-CIS (100)/WZ-CdS (100) interfaces are investigated. After relaxation the atomic positions and the bond lengths change slightly on the two interfaces. The WZ-CIS/WZ-CdS interfaces can exist stably, when the interface bonding energies are −0.481 J/m2 (bi-layer terminated interface) and −0.677 J/m2 (monolayer terminated interface). Via analysis of the density of states, difference charge density and Bader charges, no interface state is found near the Fermi level. The stronger adhesion of the monolayer terminated interface is attributed to more electron transformations and orbital hybridizations, promoting stable interfacial bonds between atoms than those on a bi-layer terminated interface.

Point defects in hexagonal germanium carbide monolayer: A first-principles calculation

On the basis of first-principles plane-wave calculations, we investigated the electronic and magnetic properties of various point defects including single Ge and C vacancies, Ge+C divacancy, Ge↔C antisites and the Stone–Wales (SW) defects in a GeC monolayer. We found that various periodic vacancy defects in GeC single layer give rise to crucial effects on the electronic and magnetic properties. The band gaps of GeC monolayer vary significantly from 0.308eV to 1.738eV due to the presence of antisites and Stone–Wales defects. While nonmagnetic ground state of semiconducting GeC turns into metal by introducing a carbon vacancy, it becomes half-metal by a single Ge vacancy with high magnetization (4μB) value per supercell. All the vacancy types have zero net magnetic moments, except single Ge vacancy.

Adsorption of alkali and alkaline-earth metal atoms on stanene: A first-principles study

This paper presents a study on the adsorption of alkali and alkaline-earth metal atoms on single-layer stanene with different levels of coverage using first-principles plane wave calculations within spin-polarized density functional theory. The most favorable adsorption site for alkali atoms (Li, Na, K) were found to be the hollow site similar to other group IV single-layers, but the case of alkaline-earths on stanene is different from silicene and germanene. Whereas Mg and Ca are bound to stanene at hollow site, the bridge site is found to be energetically favorable for Be adatom. All adsorbed atoms are positively charged due to the charge transfer from adatom to stanene single-layer. The semimetallic bare stanene become metallic except for Be adsorption. The Beryllium adsorption give rise to non-magnetic semiconducting ground state. Our results illustrate that stanene has a reactive and functionalizable surface similar to graphene or silicene.

Adsorption and Diffusion of Lithium on Monolayer Transition Metal Dichalcogenides (MoS2(1–x)Se2x) Alloys

On the basis of first-principles plane-wave calculations, we examine the adsorption and diffusion of lithium on the hexagonal MoS2(1–x)Se2x monolayers with variation of x for 0.00, 0.33, 0.50, 0.66, and 1.00. We find that the lowest energy adsorption positions of Li adatom is at the top site of Mo atom in both MoS2 and MoSe2 monolayers, while Li moves through the Mo—S bond for MoS2(1–x)Se2x. While bare MoS2(1–x)Se2x compounds are nonmagnetic semiconductor and its energy band gap varies with x, they can be metallized by Li adsorption. NEB calculation results show that their energy barriers make them suitable for using in electrode materials. The lithium adsorption energy is sensitive to the external strain, when we elongate the lattice constants, the adsorption energy decreases quickly. We also examine the penetration energy barrier for single lithium atom to pass through the MoS2(1–x)Se2x monolayers, this barrier is decreasing from ∼2.5 eV to ∼1.3 eV with increasing selenium concentration.

Lattice structures and electronic properties of WZ-CuInS2/MoS2 interface from first-principles calculations

Using first-principles plane-wave calculations within density functional theory, we theoretically studied the perfect WZ-CIS (100)/MoS2 (−100) interface, including the atomic structure, bonding energy and electronic properties. After relaxation the atomic positions and the bond lengths change slightly on the interface. The WZ-CIS/MoS2 interface can exist stably with the interface bonding energy about −0.65J/m2. Via analysis density of states, difference charge density and Bader charges we find that the electrons are largely redistributed on the interface, and there are some interface states near the Fermi level, which are mainly caused by In-5s orbital in the WZ-CIS region and S-3p orbital in the MoS2 region. On the interface the orbital hybridizations of different interfacial atoms highly enhance the bonding ability of the atoms. Electron transformation and orbital hybridization together promote the bonding between atoms and increase the adhesion energy of the interface.

Lattice structures and electronic properties of MO/MoSe2 interface from first-principles calculations

Using first-principles plane-wave calculations within density functional theory, we theoretically studied the atomic structure, bonding energy and electronic properties of the perfect Mo (110)/MoSe2 (100) interface with a lattice mismatch less than 4.2%. Compared with the perfect structure, the interface is somewhat relaxed, and its atomic positions and bond lengths change slightly. The calculated interface bonding energy is about −1.2J/m2, indicating that this interface is very stable. The MoSe2 layer on the interface has some interface states near the Fermi level, the interface states are mainly caused by Mo 4d orbitals, while the Se atom almost have no contribution. On the interface, Mo-5s and Se-4p orbitals hybridize at about −6.5 to −5.0eV, and Mo-4d and Se-4p orbitals hybridize at about −5.0 to −1.0eV. These hybridizations greatly improve the bonding ability of Mo and Se atom in the interface. By Bader charge analysis, we find electron redistribution near the interface which promotes the bonding of the Mo and MoSe2 layer.

Li-decorated graphyne as high-capacity hydrogen storage media: First-principles plane wave calculations

Taking into account the van der Waals correction, the characteristics of the Li-decorated graphyne as the hydrogen storage medium have been explored using first-principles plane wave calculations. We find that Li atom can be adsorbed not only over the center of large hexagon (HL site) but also over the center of small hexagon (HS site). For double-side Li decorations, there are 14H2 molecules can be adsorbed on Li-decorated graphyne primitive cell with the adsorption energy of 0.19 eV/H2. As a result, the hydrogen storage capacity of 13.0 wt% can be obtained. This suggests that the Li-decorated graphyne system can serve as a high-capacity hydrogen storage medium.

Effects of silver adatoms on the electronic structure of silicene

Abstract This paper presents the adsorption of Ag adatoms on silicene surface using first-principles plane wave calculations within density functional theory. It is obtained that silver adatoms form strong bonds with the silicene yielding significant binding energies. The bare silicene, which is a nonmagnetic semimetal, becomes either nonmagnetic metal or semiconductor depending on the number of adsorbed silver atoms. Because of the charge transfer from adatoms to silicene, bonding and antibonding π bands crossing linearly at the Fermi level shift 0.35 eV below the Fermi level for both single and trimer Ag adsorption. Ag dimer adsorbed silicene becomes a narrow gap semiconductor with Eg = 0.112 eV.

35Cl solid-state NMR of HCl salts of active pharmaceutical ingredients: structural prediction, spectral fingerprinting and polymorph recognition

A series of HCl salts of active pharmaceutical ingredients (APIs) have been characterizedvia35Cl solid-state NMR (SSNMR) spectroscopy and first-principles plane-wave DFT calculations of35Cl NMR interaction tensors.

Hydrogen Storage Capacity Study of a Li+Graphene Composite System with Different Charge States

Based on first-principles plane-wave calculations, we firstly reconfirm that the Li+graphene complex can be taken as a hydrogen storage medium with capacity of 12.8wt%. Then metal adsorption properties of this Li+graphene system with different charge states are investigated. Finally, the hydrogen storage ability of the charging system is calculated. Our calculations show that adding positive charge on a Li+graphene composite results in a conspicuous reduction of Li2s and Li2p orbital occupation with respect to the C2p state. As a result, a stronger bonding between Li and graphene is formed, and a special double-layer hydrogen adsorption structure has been found. Compared to the neutral system, utilizing the positive charged Li+graphene to store hydrogen molecules can solve the issue of clustering of metal atoms after releasing hydrogen, and can improve hydrogen storage capacity up to a gravimetric density of 20.4wt%, correspondingly one adsorbed Li atom can effectively absorb up to seven H2 molecules.

Adsorption of H atoms on cubic Er2O3 (0 0 1) surface: A DFT study

First-principles plane wave calculations based on spin-polarized density functional theory (DFT) and generalized gradient approximation (GGA) have been used to study the adsorption of H atoms on cubic Er2O3 (001) surface. We identify stable adsorption positions and find that H preferentially adsorbs on top of fourfold-hollow sites and transfers electrons to the surface, resulting in the formations of covalent bonds to the nearest neighboring four oxygen atoms. In the most energetically favorable adsorption sites, It was found that H bonds with O atoms at the cubic Er2O3 (001) surface with an adsorption energy of −295.68kJmol−1 at coverage 1/8ML, and the adsorption energy is inclined to decrease with the increase of H coverage (>1/4ML). In addition, our calculations indicate that the dissociative H atom configurations have adsorption energies that are at least 152.64kJmol−1 greater than the H2 molecule configurations on the surface. These results discussed in the context of erbium oxide slabs are employed to rationalize some processes regarding to the hydrogen isotope permeation behavior of tritium permeation barrier.

Raman-scattering measurements and first-principles calculations of strain-induced phonon shifts in monolayer MoS2

The effect of strain on the phonon modes of monolayer and few-layer MoS${}_{2}$ has been investigated by observing the strain-induced shifts of the Raman-active modes. Uniaxial strain was applied to a sample of thin-layer MoS${}_{2}$ sandwiched between two layers of optically transparent polymer. The resulting band shifts of the ${E}_{2g}^{1}$ ($\ensuremath{\sim}$$385.3\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$) and ${A}_{1g}$ ($\ensuremath{\sim}$$402.4\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$) Raman modes were found to be small but observable. First-principles plane-wave calculations based on density functional perturbation theory were used to determine the Gr\uneisen parameters for the ${E}_{1g}$, ${E}_{2g}^{1}$, ${A}_{1g}$, and ${A}_{2u}$ modes and predict the experimentally observed band shifts for the monolayer material. The polymer--MoS${}_{2}$ interface is found to remain intact through several strain cycles. As an emerging 2D material with potential in future nanoelectronics, these results have important consequences for the incorporation of thin-layer MoS${}_{2}$ into devices.