Two-component Density Functional Theory Research Articles

Spin–orbit coupling within a two-component density functional theory approach: theory, implementation and first applications

An implementation of spin–orbit coupling within a two-component generalization of the density functional code MAGIC is described. The spin–orbit operator is represented in the effective one-electron mean-field approximation and included into the Fock matrix within an iterative self-consistent scheme. First tests have been carried out for the spin–orbit splitting of several atoms. The spin–orbit effect on the bond distance and harmonic frequency of some diatomics has also been determined. This scheme allows to include spin–orbit in a simple way and can be efficiently used to treat large systems.

Anisotropy in the Positron 2D Angular Correlation of Annihilation Radiation for Singly Negative Divacancies in Si

Interesting features of positron two-dimensional angular correlation of annihilation radiation (2D-ACAR) distribution for singly negative divacancies in Si are studied experimentally and theoretically. Anisotropy of the distribution is successfully detected for a specimen with aligned divacancies and is well reproduced by first-principles calculations based on the two-component density-functional theory. The present calculation demonstrates that the anisotropy reflects the characteristic distribution of electrons around the divacancies, indicating that the 2D-ACAR is an effective tool to provide microscopic information on vacancy-type defects.

First-principles calculation of positron annihilation characteristics at metal vacancies.

Annihilation characteristics for positrons trapped at metal vacancies are calculated from first principles. The calculations are based on different implementations of the two-component density-functional theory, and different numerical methods to solve the ensuing Kohn-Sham equations have been employed. The convergence of the positron annihilation characteristics calculated within different schemes is discussed, and the positron lifetimes obtained are compared with experiment.

Lifetimes of positrons trapped at Si vacancies.

We present first-principles calculations on positron lifetimes at various vacancies in Si. Lattice relaxation and electron redistribution caused by the vacancy and by the positron are included using the two-component density-functional theory. The calculated lifetimes are in agreement with the experimental data for the monovacancies and the divacancies and provide a new assignment of the longer lifetimes measured previously to stable multivacancies. \textcopyright{} 1996 The American Physical Society.

FULLY SELF-CONSISTENT CALCULATION OF POSITRON STATES OF MONOVACANCY IN ALUMINUM

The discrete variational method and embedded-cluster model within the framework of the two-component density functional theory and firstprinciple method are used to calculate the positron states of monovacancy in aluminum. The effect of the crystal field in which the cluster is embedded, magnitude of the cluster and frozen-core density approximation on the distribution of positron density and the positron annihilation characteristics are analyzed. The influence of the fully self-consistent scheme and the conventional scheme on the calculation of positron states in solids is discussed.

A fully self-consistent calculation for positron states: application to aluminium

A fully self-consistent scheme based on the two-component density-functional theory and an embedded-cluster model within the framework of the discrete variational method has been developed for calculating positron states in solids. As an example, aluminium is tested. The changes of the electronic structures and positron states for an aluminium vacancy due to the electron-positron interaction are presented. The effects of the atomic relaxations on the positron annihilation characteristics are considered. The results are also compared with former calculations and the conventional scheme.

Two-component density functional theory of positron binding to negative ions

The problem of binding in positron-negative ion systems has been addressed via two-component density functional theory. Calculations have been performed within the local density approximation for electron exchange-correlation as well as for the electron-positron correlation potential using a self-interaction corrected version of the density functional equations. Our results indicate that a positron forms a stable bound state with the negative ions Li −,B −,C −,O −,F − and Cl − with respect to dissociation into a negative ion and a positron or a neutral atom and positronium. Inclusion of electron-positron correlation deepens the positron bound state and stabilizes the system compared to earlier exchange-only calculations.

Electron-positron density-functional theory.

A two-component density-functional theory is presented for electron-positron systems. The phase diagram of a two-component Fermi-Coulomb system is discussed, and explicit expressions are derived for exchange-correlation functionals for use in the local-density approximation. The scheme is then applied in a fully self-consistent calculation of electron and positron densities in atomic vacancies in metals, treated in the jellium model. Comparison with conventional calculations, which do not meet true electron-positron self-consistency, reveals considerable changes in the density distributions. However, we demonstrate that there are cancellation effects which render the corresponding changes in observable annihilation characteristics relatively small.

Two-component density-functional theory: Application to positron states.

A quantitative approach to calculating properties of inhomogeneous two-component Coulomb-Fermi systems is presented. As an application, the ground-state electronic structure of a jellium vacancy containing a trapped positron is calculated self-consistently. While the resulting density profiles and energetics are quite different from those obtained neglecting cross correlations, the conventional estimates for the annihilation rates are shown to remain valid, due to canceling effects of the increase in the mean electron density and the decrease in short-range screening.