Coherent potential approximation

About: Coherent potential approximation is a research topic. Over the lifetime, 1930 publications have been published within this topic receiving 36805 citations.

Quantum transport theory in the coherent-potential approximation

Abstract: A quantum formulation of the electrical conductivity of a disordered alloy is made in the coherent-potential approximation (CPA). The formalism is applicable to the case where the one-electron Hamiltonian (or its suitably renormalized form) depends additively on the configurations of individual sites. The configurational average of the vertex function which involves the random one-electron current operator is evaluated in the CPA by introducing the effective (or coherent) current operator, which is periodic but energy-dependent. It is shown that the case where the vertex correction to the vertex function vanishes is rather exceptional but that the kernel of the integral equation determining the vertex correction can be written in the separable type in the CPA. The correspondence between the present theory and the semiclassical Boltzmann theory is investigated in detail.

Tight-binding branch-point energies and band offsets for cubic InN, GaN, AlN, and AlGaN alloys

Abstract: Starting with empirical tight-binding band structures, the branch-point (BP) energies and resulting valence band offsets for the zincblende phase of InN, GaN, and AlN are calculated from their k-averaged midgap energy. Furthermore, the directional dependence of the BPs of GaN and AlN is discussed using the Green's function method of Tersoff. We then show how to obtain the BPs for binary semiconductor alloys within a band-diagonal representation of the coherent potential approximation and apply this method to cubic AlGaN alloys. The resulting band offsets show good agreement to available experimental and theoretical data from the literature. Our results can be used to determine the band alignment in isovalent heterostructures involving pure cubic III-nitrides or AlGaN alloys for arbitrary concentrations.

Exact muffin tin orbital based first-principles method for electronic-structure and electron-transport simulation of device materials

Abstract: The exact muffin tin orbital (EMTO) method features high efficiency and accuracy for first-principles simulations with density functional theory. In this paper we report our implementation of the EMTO method for electronic-structure and quantum transport simulation of device materials. We consider a device-material structure with a central device region in contact with different semi-infinite electrodes. Based on the Green's function method, the infinite device, nonperiodic in transport direction, is transformed into a calculable finite material system by treating the semi-infinite electrodes with electrode self-energies, and the Green's function of the device region is calculated with an efficient recursive technique. In the present implementation we adopt the spherical cell approximation to treat the electrostatics, and we solve the electrostatic potential of the finite device region by enforcing the boundary conditions to the known potential of electrode materials. The coherent potential approximation is incorporated for treating the atomic disorders inevitable in realistic materials, and the effects of multiple disorder scattering on electron transport are accounted for by vertex correction for simulating disordered electronic devices. To demonstrate the capability of the present implementation, we calculate the monolayer two-dimensional material MoS2 and black phosphorus, and study the spin-dependent tunneling in the Fe/MgO/Fe magnetic tunneling junction. We find the EMTO electronic structures of the calculated systems agree well with the results of the projector augmented wave method. The EMTO transport simulation produces the important spin-filtering effect of the Fe/MgO/Fe junction and the important influence of the interfacial disorders on the spin-dependent tunneling, agreeing well with previous theoretical and experimental studies. The implementation of the EMTO based device simulator provides an effective simulation tool for simulating both ordered and disordered device materials, extending the capability for theoretical design of electronic devices from first principles.

Model calculations for the vibrational anomalies of a disordered Lennard–Jones solid

Abstract: Using a modified version of the two-site coherent potential approximation (CPA), also known as effective medium approximation (EMA), we can calculate the density of states (DOS) of a disordered rare-gas-solid modelled by a Lennard–Jones potential. As input we use the radial pair distribution of a pertinent molecular-dynamics simulation of Rahman et al. The resulting DOS agrees well with that of the simulation. The DOS exhibits an anomalous enhanced low-frequency contribution (“boson peak”). We investigate and discuss the influence of the quenched structure on this anomaly and on the resulting sound velocity.