arXiv subjects

Petr A. Khomyakov

Publications and source records attributed to Petr A. Khomyakov.

11 recordsLinked to original sources

arXiv2019

QuantumATK: An integrated platform of electronic and atomic-scale modelling tools

QuantumATK is an integrated set of atomic-scale modelling tools developed since 2003 by professional software engineers in collaboration with academic researchers. While different aspects and individual modules of the platform have been previously presented, the purpose of this paper is to give a general overview of the platform. The QuantumATK simulation engines enable electronic-structure calculations using density functional theory or tight-binding model Hamiltonians, and also offers bonded or reactive empirical force fields in many different parametrizations. Density functional theory is implemented using either a plane-wave basis or expansion of electronic states in a linear combination of atomic orbitals. The platform includes a long list of advanced modules, including Green's-function methods for electron transport simulations and surface calculations, first-principles electron-phonon and electron-photon couplings, simulation of atomic-scale heat transport, ion dynamics, spintronics, optical properties of materials, static polarization, and more. Seamless integration of the different simulation engines into a common platform allows for easy combination of different simulation methods into complex workflows. Besides giving a general overview and presenting a number of implementation details not previously published, we also present four different application examples. These are calculations of the phonon-limited mobility of Cu, Ag and Au, electron transport in a gated 2D device, multi-model simulation of lithium ion drift through a battery cathode in an external electric field, and electronic-structure calculations of the composition-dependent band gap of SiGe alloys.

cond-mat.mtrl-sci↗

arXiv2017

First-principles Green's-function method for surface calculations: a pseudopotential localized basis set approach

We present an efficient implementation of a surface Green's-function method for atomistic modeling of surfaces within the framework of density functional theory using a pseudopotential localized basis set approach. In this method, the system is described as a truly semi-infinite solid with a surface region coupled to an electron reservoir, thereby overcoming several fundamental drawbacks of the traditional slab approach. The versatility of the method is demonstrated with several applications to surface physics and chemistry problems that are inherently difficult to address properly with the slab method, including metal work function calculations, band alignment in thin-film semiconductor heterostructures, surface states in metals and topological insulators, and surfaces in external electrical fields. Results obtained with the surface Green's-function method are compared to experimental measurements and slab calculations to demonstrate the accuracy of the approach.

cond-mat.mtrl-sci↗

arXiv2015

Compositional bowing of band energies and their deformation potentials in strained InGaAs ternary alloys: a first-principles study

Using first-principles calculations, we show that the conduction and valence band energies and their deformation potentials exhibit a non-negligible compositional bowing in strained ternary semiconductor alloys such as InGaAs. The electronic structure of these compounds has been calculated within the framework of local density approximation and hybrid functional approach for large cubic supercells and special quasi-random structures, which represent two kinds of model structures for random alloys. We find that the predicted bowing effect for the band energy deformation potentials is rather insensitive to the choice of the functional and alloy structural model. The direction of bowing is determined by In cations that give a stronger contribution to the formation of the In$_{x}$Ga$_{1-x}$As valence band states with $x\gtrsim 0.5$, compared to Ga cations.

cond-mat.mtrl-sci↗

arXiv2015

The reversible lithiation of SnO: a three-phase process

A high reversible capacity is a key feature for any rechargeable battery. In the lithium-ion battery technology, tin-oxide anodes do fulfill this requirement, but a fast loss of capacity hinders a full commercialization. Using first-principles calculations, we propose a microscopic model that sheds light on the reversible lithiation/delithiation of SnO and reveals that a sintering of Sn causes a strong degradation of SnO-based anodes. When the initial irreversible transformation ends, active anode grains consist of Li-oxide layers separated by Sn bilayers. During the following reversible lithiation, the Li-oxide undergoes two phase transformations that give rise to a Li-enrichment of the oxide and the formation of a layered SnLi composite. We find that the model-predicted anode volume expansion and voltage profile agree well with experiment, and a layered anode grain is highly-conductive and has a theoretical reversible capacity of 4.5 Li atoms per a SnO host unit. The model suggests that the grain structure has to remain layered to sustain its reversible capacity and a thin-film design of battery anodes could be a remedy for the capacity loss.

cond-mat.mtrl-sci↗

arXiv2013

Field effect doping of graphene in metal|dielectric|graphene heterostructures: a model based upon first-principles calculations

We study how the Fermi energy of a graphene monolayer separated from a conducting substrate by a dielectric spacer depends on the properties of the substrate and on an applied voltage. An analytical model is developed that describes the Fermi level shift as a function of the gate voltage, of the substrate work function, and of the type and thickness of the dielectric spacer. The parameters of this model, that should describe the effect of gate electrodes in field-effect devices, can be obtained from density functional theory (DFT) calculations on single layers or interfaces. The doping of graphene in metal|dielectric|graphene structures is found to be determined not only by the difference in work function between the metal and graphene and the dielectric properties of the spacer but potential steps that result from details of the microscopic bonding at the interfaces also play an important role. The doping levels predicted by the model agree very well with the results obtained from first-principles DFT calculations on metal|dielectric|graphene structures with the metals Al, Co, Ni, Cu, Pd, Ag, Pt or Au, and a h-BN or vacuum dielectric spacer.

cond-mat.mes-hall↗

arXiv2011

Electrostatic doping of graphene through ultrathin hexagonal boron nitride films

When combined with graphene, hexagonal boron nitride (h-BN) is an ideal substrate and gate dielectric with which to build metalh-BN|graphene field-effect devices. We use first-principles density functional theory (DFT) calculations for Cu|h-BN|graphene stacks to study how the graphene doping depends on the thickness of the h-BN layer and on a potential difference applied between Cu and graphene. We develop an analytical model that describes the doping very well, allowing us to identify the key parameters that govern the device behaviour. A predicted intrinsic doping of graphene is particularly prominent for ultrathin h-BN layers and should be observable in experiment. It is dominated by novel interface terms that we evaluate from DFT calculations for the individual materials and for interfaces between h-BN and Cu or graphene.

cond-mat.mtrl-sci↗

arXiv2011

Ni(111)|Graphene|h-BN Junctions as Ideal Spin Injectors

Deposition of graphene on top of hexagonal boron nitride (h-BN) was very recently demonstrated while graphene is now routinely grown on Ni. Because the in-plane lattice constants of graphite, h-BN, graphite-like BC2N and of the close-packed surfaces of Co, Ni and Cu match almost perfectly, it should be possible to prepare ideal interfaces between these materials which are respectively, a semimetal, insulator, semiconductor, ferromagnetic and nonmagnetic metals. Using parameter-free energy minimization and electronic transport calculations, we show how h-BN can be combined with the perfect spin filtering property of Ni|graphite and Co|graphite interfaces to make perfect tunnel junctions or ideal spin injectors (SI) with any desired resistance-area product.

cond-mat.mtrl-sci↗

arXiv2007

Substrate-induced bandgap in graphene on hexagonal boron nitride

We determine the electronic structure of a graphene sheet on top of a lattice-matched hexagonal boron nitride (h-BN) substrate using ab initio density functional calculations. The most stable configuration has one carbon atom on top of a boron atom, the other centered above a BN ring. The resulting inequivalence of the two carbon sites leads to the opening of a gap of 53 meV at the Dirac points of graphene and to finite masses for the Dirac fermions. Alternative orientations of the graphene sheet on the BN substrate generate similar band gaps and masses. The band gap induced by the BN surface can greatly improve room temperature pinch-off characteristics of graphene-based field effect transistors.

cond-mat.mtrl-sci↗

arXiv2006

Stability of conductance oscillations in monatomic sodium wires

We study the stability of conductance oscillations in monatomic sodium wires with respect to structural variations. The geometry, the electronic structure and the electronic potential of sodium wires suspended between two sodium electrodes are obtained from self-consistent density functional theory calculations. The conductance is calculated within the framework of the Landauer-Bütttiker formalism, using the mode-matching technique as formulated recently in a real-space finite-difference scheme [Phys. Rev. B \textbf{70}, 195402 (2004)]. We find a regular even-odd conductance oscillation as a function of the wire length, where wires comprising an odd number of atoms have a conductance close to the quantum unit $G_0=e^2/π\hbar$, and even-numbered wires have a lower conductance. The conductance of odd-numbered wires is stable with respect to geometry changes in the wire or in the contacts between the wire and the electrodes; the conductance of even-numbered wires is more sensitive. Geometry changes affect the spacing and widths of the wire resonances. In the case of odd-numbered wires the transmission is on-resonance, and hardly affected by the resonance shapes, whereas for even-numbered wires the transmission is off-resonance and sensitive to the resonance shapes. Predicting the amplitude of the conductance oscillation requires a first-principles calculation based upon a realistic structure of the wire and the leads. A simple tight-binding model is introduced to clarify these results.

cond-mat.mtrl-sci↗

arXiv2005

Operator method for solution of the Schrödinger equation with the rational potential

The eigenvalue problem for one-dimensional Schrödinger equation with the rational potential is numerically solved by the operator method. We show that the operator method, applied for solving the Schrödinger equation with the nonpolynomial structure of the Hamiltonian, becomes more efficient if a nonunitary transformation of the Hamiltonian is used. We demonstrate on numerous examples that this method can handle both perturbative and nonperturbative regimes with very high accuracy and moderate computational cost.

quant-ph↗

arXiv2004

Real space finite difference method for conductance calculations

We present a general method for calculating coherent electronic transport in quantum wires and tunnel junctions. It is based upon a real space high order finite difference representation of the single particle Hamiltonian and wave functions. Landauer's formula is used to express the conductance as a scattering problem. Dividing space into a scattering region and left and right ideal electrode regions, this problem is solved by wave function matching (WFM) in the boundary zones connecting these regions. The method is tested on a model tunnel junction and applied to sodium atomic wires. In particular, we show that using a high order finite difference approximation of the kinetic energy operator leads to a high accuracy at moderate computational costs.

cond-mat.mtrl-sci↗