Herbert Schlosser

Multilayer relaxation and surface structure of ordered alloys

Using BFS, a new semiempirical method for alloys, we study the surface structure of fcc ordered binary alloys in the L12 structure (Ni3Al and Cu3Au). We show that the surface energy is lowest for the mixed-composition truncation of the low-index faces of such systems. Also, we present results for the interlayer relaxations for planes close to the surface, revealing different relaxations for atoms of different species producing a rippled surface layer.

Cohesive energy-lattice constant and bulk modulus-lattice constant relationships: Alkali halides, Ag halides, Tl halides

Abstract In this note we present two expressions relating the cohesive energy, E coh , and the zero pressure isothermal bulk modulus, B 0 , of the alkali halides, Ag halides and Tl halides, with the nearest neighbor distances, d nn . First, we show that the product E coh d nn within families of halide crystals with common crystal structure is to a good approximation constant, with maximum rms deviation of ±2%. Secondly, we demonstrate that within families of halide crystals with a common cation and common crystal structure the product B 0 d nn 3.5 is to a good approximation constant, with maximum rms deviation of ±1.36%.

An accurate analytic approximation to the non-linear change in volume of solids with applied pressure

An accurate analytic expression for the non-linear change of the volume, Delta V/V0, of a solid as a function of applied pressure, P, is of great interest in high-pressure experimentation. The authors have found that the two-parameter analytic expression, ( Delta V/V0)=(1/ alpha )ln(1+ beta P), fits the experimental Delta V/V0 data, to within a few per cent over the entire experimentally attainable pressure range. Results are presented for 24 different materials including metals, ceramic semiconductors, polymers, ionic and rare-gas solids.

Pseudopotential Approaches to Localized Orbitals for Polyatomic Systems

We present a method for constructing optimized pseudopotentials for general polyatomic systems which yield the “smoothest” orbitals localized in particular regions of space. (“Smoothest” orbitals are those for which the expectation value of the kinetic energy operator is a minimum.) We specifically consider the general case in which one can have several occupied orbitals localized in a particular region, rather than a single orbital. Recently, Anderson presented a pseudopotential formalism for constructing localized orbitals for a single isolated band in a polyatomic system. We have extended his formalism to the general multiorbital case, and show that for a specific choice of pseudopotential the Anderson equation yields optimal orbitals. We also show that the Huckel form of the Anderson pseudopotential equation yields identical eigenvalues (neglecting terms of order S2) to the optimal form, and orbitals differing from optimal orbitals by terms linear in S. The correction terms to the Huckel orbitals are ...

A thermodynamic model for pressurized solids

A thermodynamic model for solids under pressure is developed by assuming the universal equation of state and that under zero pressure the free energy is equal to the harmonic crystal (Debye) free energy. The model is applied to gold. In the case of nanocrystals this model reproduces the observed enhancement of the isobaric heat capacity and of the thermal expansion. Our model calculations are free of the ambiguities and inconsistencies connected with the Gruneisen equation, which was used in previous theoretical work.

THE ANALYSIS OF HIGH PRESSURE EXPERIMENTAL DATA

Abstract This letter is concerned with the analysis of high pressure experimental data. We demonstrate that In H plots based on the Vinet et al. universal equation of state (EOS) are a simple sensitive means for identifying anomalous P-V data in high pressure experiments, and for detecting structural and phase transitions in solids subjected to high pressure.

Simplified Multiconfiguration Self‐Consistent‐Field Theory for Localized Orbitals. II Fluctuating Orbitals

We develop a simplified version of the fluctuating orbital multiconfiguration self‐consistent‐field theory (MC‐SCF‐FLO) for localized orbitals of Gilbert. We proceed by analyzing the operators and matrix elements in powers of the overlap, neglecting terms quadratic and higher in overlap. This eliminates many of the terms found in the complete theory. The matrix elements of the orbital operators are particularly simple since all strictly environmental terms and many of the subsystem‐environment interaction terms vanish. The orbital and secular equations are then decomposed into equations for a system coupled to its environment.

Localized Orbitals for Polyatomic Systems. II. Open Shell Case

We present a generalization of the Adams—Gilbert approach for constructing localized Hartree—Fock (HF) orbitals from the closed shell single Slater determinant case to the case where one has several open shells of different symmetry in addition to closed shells of electrons. Our starting point is the open shell HF formalism discussed by Roothaan and Huzinaga. We then apply appropriate localization operators to construct the localized AG orbitals, and also develop the resulting equations in powers of the overlap. Finally, we present several perturbation‐iteration schemes for solving the open shell Adams—Gilbert equations, and comment on pseudopotential methods for construction of localized orbitals.

Universal energy relations and metal/ceramic interfaces

Known general relationships between pertinent variables are applied to investigate metal-ceramic interfaces. The adhesive energy is determined. The electronic exchange-correlation energy is found to be the dominant attractive term in the total energy. Results for the adhesive energy are obtained for junctions of all combinations of the low index surfaces of Al,Na, Mg, and Zn. This leads to a variety of curves, all with a single minimum of separation and equilibrium binding energy. Scaling results for 10 contacts fall closely onto a single curve, a universal energy relation for adhesion. The scaled chemisorption curves fall accurately on the same universal form that was found for adhesion. For the case of cohesion, all-first principle results are scaled and again all scaled curves for a variety of metals fall accurately on the universal form for adhesion and chemisorption. An intimate relationship between the energetics of solids and molecules is inferred.

Pseudopotential method for the direct construction of localized orbitals by multiconfiguration self-consistent field theory

Abstract The orbital equations for the direct construction of localized fixed orbitals by multiconfiguration self-consistent field theory (MCSCF-FXO) are transformed without approximation into pseudopotential form by a two-step process. First the utilization of a particular family of localization is shown to separate the set of orbital equations into two sets of coupled equations, one describing “valence” orbitals and one describing “core” orbitals. In addition we obtain by appropriate choice of localization potential three different sets of MCSCF-FXO orbitals, namely: maximally screened, “one-center” and “intermediate” orbitals. In the second step the orbital equations are transformed into pseudopotential form and explicit non-local pseudopotentials yielding and core orbitals are obtained. Finally, several different physically motivated approximations to the exact pseudopotentials, and the frozen-core approximation are discussed.