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Influence of gradient amendments of kinetic energy in computation of surface characteristics of metals

Keywords:

V.L. Glushkov – Assistant, Department of Physics, Bauman Moscow State Technical University
O.S. Erkovitch – Ph.D. (Phys.-Math.), Department of Physics,Associate Professor,  Bauman Moscow State Technical University


This work is devoted to the study of the effect of gradient corrections on the kinetic energy functional in calculating the surface energy of a metal surface within the framework of the density functional theory. The electron density near the metal was calculated by a variational method for two test functions differing with allowance for the Friedel oscillations. The metal surface is considered in the model of a metal in which the positive charges are replaced by a uniform charge background of density.The calculation of the surface energy taking into account the gradient corrections to the inhomogeneity of the electron gas for the kinetic energy of the second and fourth order is carried out. The contribution of the ionic crystal lattice was taken into account in the framework of perturbation theory. The Ashcroft pseudopotential was chosen as the ion potential. An analysis of the expediency of using the gradient expansion of the kinetic energy was carried out on the basis of a comparison of the calculated surface characteristics and their experimental values for the selected metals. The surface characteristics of the metal, such as the work function and the height of the potential barrier, are obtained for two types of test functions for the electron density.The orientation of the faces of the crystal surface also affects the values of the metal surface.
An investigation of the effect of gradient corrections on the kinetic energy of a number of metals, taking into account the discreteness of the crystal lattice, within the framework of the density function method, showed that gradient corrections of the fourth order for the exponential function of the electron density distribution leads to an insignificant improvement in the results of calculating the surface characteristics, in comparison with the experimental values.For the test function of the electron density, which takes Friedel oscillations into account, the contribution of gradient corrections of high order is significant and makes it possible to significantly improve the agreement between the calculated values of the surface characteristics and the experimental data.

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