Search query: Ab initio Green 

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abstract: We herein present a first principles formulation of the Green Kubo method that allows the accurate assessment of the phonon thermal conductivity of solid semiconductors and insulators in equilibrium ab initio molecular dynamics calculations. Using the virial for the nuclei, we propose a unique ab initio definition of the heat flux. Accurate size and time convergence are achieved within moderate computational effort by a robust, asymptotically exact extrapolation scheme. We demonstrate the capabilities of the technique by investigating the thermal conductivity of extreme high and low heat conducting materials, namely, Si (diamond structure) and tetragonal ZrO_{2}
author_names: Christian Carbogno

Rampi Ramprasad

Matthias Scheffler
title: Ab Initio Green Kubo Approach for the Thermal Conductivity of Solids.
venue: Physical review letters
year: 2017

abstract: The Green Kubo theory of thermal transport has long be considered incompatible with modern simulation methods based on electronic structure theory, because it is based on such concepts as energy density and current, which are ill defined at the quantum mechanical level. Besides, experience with classical simulations indicates that the estimate of heat transport coefficients requires analysing molecular trajectories that are more than one order of magnitude longer than deemed feasible using ab initio molecular dynamics. In this paper we report on recent theoretical advances that are allowing one to overcome these two obstacles. First, a general gauge invariance principle has been established, stating that thermal conductivity is insensitive to many details of the microscopic expression for the energy density and current from which it is derived, thus permitting to establish a rigorous expression for the energy flux from Density Functional Theory, from which the conductivity can be computed in practice. Second, a novel data analysis method based on the statistical theory of time series has been proposed, which allows one to considerably reduce the simulation time required to achieve a target accuracy on the computed conductivity. These concepts are illustrated in detail, starting from a pedagogical introduction to the Green Kubo theory of linear response and transport, and demonstrated with a few applications done with both classical and quantum mechanical simulation methods.
author_names: Stefano Baroni

Riccardo Bertossa

Loris Ercole

Federico Grasselli

Aris Marcolongo
title: Heat transport in insulators from ab initio Green Kubo theory
year: 2018

author_names: Stefano Baroni
title: Car and Parrinello meet Green and Kubo: simulating atomic heat transport from equilibrium ab initio molecular dynamics
year: 2017

abstract: Abstract The structural and dynamical properties of liquid alloys are directly related to their solidification process, and consequently to the properties of as cast solid alloys. Ab initio molecular dynamics is a powerful tool that can be used to study both of these factors. Thus, in this work, TiZrNbHfTa and VZrMoHfW liquid equiatomic alloys, exclusively consisting of transition metal (TM) elements, are studied using ab initio molecular dynamics via the CP2K software package; partial pair correlation functions (PPCFs) are calculated, and their parameters are discussed. The calculated densities of these alloys are shown to be close to the ideal mixture densities. The analysis of the PPCFs is performed to predict the single phase high entropy alloy (HEA) formation. The obtained results agree with the semi empirical phase formation rules. The diffusivities of the elements are calculated using the Green Kubo relation and the mean square displacement (MSD) plot. The diffusivity is shown to decrease as the atomic mass and radius increase. The scattering process of different types of atoms in TiZrNbHfTa and VZrMoHfW are also discussed.
author_names: I A Balyakin

Boris Gelchinski

Andrej A Rempel
title: Ab initio molecular dynamics study of TiZrNbHfTa and VZrMoHfW liquid alloys
year: 2019

abstract: Transport properties of permalloy doped with V, Co, Pt, and Au are explored via ab initio calculations. The Kubo Bastin formula is evaluated within the fully relativistic Korringa Kohn Rostoker Green function formalism. Finite temperature effects are treated by means of the alloy analogy model. It is shown that the fact that the host is disordered and not crystalline has a profound effect on how the conductivities characterizing the anomalous Hall effect and the spin Hall effect depend on the dopant concentration. Several relationships between quantities characterizing charge and spin transport are highlighted. The decrease of the longitudinal charge conductivity with increasing doping depends on the dopant type, following the sequence Co Au Pt V. The dependence of the anomalous Hall and spin Hall conductivities on the dopant concentration is found to be non monotonic. Introducing a finite temperature changes the overall trends significantly. The theoretical results are compared with available experimental data.
author_names: Ondrej Sipr

S Wimmer

S Mankovsky

Hubert Ebert
title: Transport properties of doped permalloy via ab initio calculations: Effect of host disorder
year: 2019

abstract: Here, given the unique optical properties of LiF, it is often used as an observation window in high temperature and pressure experiments; hence, estimates of its transmission properties are necessary to interpret observations. Since direct measurements of the thermal conductivity of LiF at the appropriate conditions are difficult, we resort to molecular simulation methods. Using an empirical potential validated against ab initio phonon density of states, we estimate the thermal conductivity of LiF at high temperatures (1000 4000 K) and pressures (100 400 GPa) with the Green Kubo method. We also compare these estimates to those derived directly from ab initio data. To ascertain the correct phase of LiF at these extreme conditions, we calculate the (relative) phase stability of the B1 and B2 structures using a quasiharmonic ab initio model of the free energy. We also estimate the thermal conductivity of LiF in an uniaxial loading state that emulates initial stages of compression in high stress ramp loading experiments and show the degree of anisotropy induced in the conductivity due to deformation.
author_names: Rosemary E Jones

D K Ward
title: Estimates of crystalline LiF thermal conductivity at high temperature and pressure by a Green Kubo method
year: 2016

abstract: The experimental unexpected large Seebeck coefficient in SrTiO3 (STO) cannot be reproduced theoretically by the conventional Bloch Boltzmann transport with electron phonon coupling calculated perturbatively, indicating a failure of Fermi liquid picture in STO and ill treatment of polaronic states. Starting from many body interaction picture, the polaronic states can be precisely described by the method of cumulant expansion of retarded Green's function. By applying Kubo Greenwood method, we found that the mysterious Seebeck coefficient can be fully described by a combination of polarons and Fermi liquid. The coexistence of two types of quasi particles are attributed to the multi band nature of t2g orbitals. Polarons are formed from the one with heavier electronic effective mass, while the one with lighter effective mass is renormalized into Fermi liquid quasi particles. Our method provides a practical way to study the effect of strong electron phonon coupling on transport properties from first principles.
author_names: Jichang Ren

Jian-Sheng Wang
title: Origin of unexpected large Seebeck effect in SrTiO3: nonperturbative polaron study from ab initio cumulant expansion.
year: 2018

abstract: The electronic structure and magnetic properties of rocksalt type CaC compound are studied by means of first principles calculations. The B1 type calcium monocarbide is a metastable, nearly half metallic ferromagnetic compound, with a magnetic moment of 1.81 m B/f.u. and a negative Fermi level spin polarization of 50% The estimated Curie temperature exceeds the room temperature. The electronic, magnetic and spin polarized transport properties of CaC/MgS/CaC (0 0 1) heterostructures are investigated by using a first principles Green's function technique for layered structures in conjunction with the Kubo Landauer formalism. The magnetism of CaC (0 0 1) electrodes is robust while the Fermi level spin polarization of interfacial CaC layers at CaC/MgS (0 0 1) interfaces increases over the bulk value. The localized states formed at CaC/MgS (0 0 1) interfaces strongly enhance the minority spin ferromagnetic state conductance. The current spin polarization reaches values as high as 99% Very large magnetoresistance ratios, above 104% are in evidence. The highly magnetoresistive effect observed for CaC/MgS/CaC (0 0 1) heterojunctions together with the robust ferromagnetism of CaC (0 0 1) electrodes make this system attractive in the context of spin electronics.
author_names: Petru Vlaic

Emil Burzo

Karel Carva
title: Spin polarized transport utilizing d 0 ferromagnetism: an ab initio study of CaC/MgS/CaC (0 0 1) heterojunctions
year: 2015

abstract: Quantum simulation methods based on density functional theory are currently deemed to be unfit to cope with atomic thermal transport in materials within the Green Kubo formalism. In contrast with this belief, we derive an expression for the adiabatic energy flux from density functional theory, that permits the ab initio simulation of atomic thermal transport using equilibrium molecular dy namics. The resulting thermal conductivity is shown to be unaffected by the inherent ill definedness of quantum mechanical energy densities and currents. Our new methodology is demonstrated by comparing results from ab initio and classical molecular dynamics simulations of a model liquid Argon system, for which accurate inter atomic potentials are derived by the force matching method, and finally applied to compute the thermal conductivity of heavy water at ambient conditions.
author_names: Aris Marcolongo
title: Theory and ab initio simulation of atomic heat transport
year: 2014

abstract: We develop a formalism for the evaluation of conduction eigenchannels of atomic sized contacts from first principles. The multiple scattering Korringa Kohn Rostoker Green's function method is combined with the Kubo linear response theory. Solutions of the eigenvalue problem for the transmission matrix are proven to be identical to eigenchannels introduced by Landauer and B\"uttiker. Applications of the method are presented by studying ballistic electron transport through Cu, Pd, Ni, and Co single atom contacts. We show in detail how the eigenchannels are classified in terms of irreducible representations of the symmetry group of the system as well as by orbital contributions when the channels' wave functions are projected on the contact atom.
author_names: Alexei Bagrets

N Papanikolaou

Ingrid Mertig
title: Conduction eigenchannels of atomic sized contacts: Ab initio KKR Green's function formalism.
year: 2007