Reliability of Various Empirical Potential Methods

Self Cite

The pair-correlation functions of liquid Fe, Cu, Ag, Au, and V are calculated from empirically determined potentials obtained from the solid state of these substances. The calculations use Percus-Yevick theory, and comparison is made between the results using the empirical potentials obtained by Esterling-Swaroop and those of Johnson and Wilson. Reasonable agreement with the experimentally determined pair-correlation functions is obtained for Fe, Cu, and Ag with both sets of potentials. However, the results for Au and V with the Esterling-Swaroop potentials are not satisfactory. It is noted independent evidence suggests that the pair potential approximation is inadequate for these two metals. In addition, the pair-correlation function serves as a discriminator between two pair potentials for iron derived from the same phonon data.

Section: Calculationsmentioning

confidence: 99%

“…Van Heugten and de Hosson [5] have made similar calculations using, in addition, phonon data. The use of the vacancy forniation energy in a strict pair-potential model (no volumedependent terms) has been questioned [6]. I n addition, the fit to diatomic results a t very short range may lead to peculiarities in the potential [a, 61.…”

Section: Introductionmentioning

confidence: 99%

Liquid Metal Pair‐Correlation Functions from Empirical Pair Potentials

McGurn¹,

Esterling²

1981

Self Cite

On Energy‐Wave Number Characteristics F(q) in Metals as Derived from Experimental Phonon Spectra

Brosens

Derveese

Cornelis

et al. 1980

on the occasion of his 75th birthday A method to determine the energy-wa,ve number characteristic of metals directly from experimental phonon spectra is discussed with respect to the uniqueness problem, and in connection with the hypothesis of a central interatomic potential.Eine Methode zur Bestimmung der Energie-Wellenzahl-Charakteristik von Metallen direkt aus den experimentellen Phononen-Spektren wird beziiglich des Eindeutigkeitsproblems und in Verbindung mit der Annahme eines zentrosymmetrischen interatomaren Potentials diskutiert.

An Interatomic Pair Potential for Aluminium Calculation of Stacking Fault Energy

Rautioaho

1982

A potential function for aluminium is derived from phonon dispersion curves. The contribution from short-range multi-ion interactions is substracted from the phonon data, and this affecto markedly the short-range characteristics of the potential. The potential function is used for tho calculation of the energies of intrinsic and extrinsic stacking faults. Certain multi-ion contributions to these energies are also evaluated. The calculation cannot explain the experimentally observed difference between Vntr and yextr, which is attributed here to the interpretation of loop annealing observations in such faults. A re-interpretation gives approximntely 120 mJ/m2 for Iritroiluc tioriOur knowledge of atomic interactions has increased greatly during the last twenty years. The pair potential approach or its equivalent, the second-order pseudopotential approach, appear to be appropriate only for simple metals, and are in suspect in the case of noble or transition metals. Of the technically important metals, only a hmininni belongs to the first group, but even its treatment suffers from limitations. The selection of the pseudopotential and the screening function is not unique, and for this reason a variety of more or less fundamental pair potentials have been constructed for this metal. I n addition, those third-and higher-order terms in electron-ion interaction which contribute to pairwise atomic interaction are generally omitted from the calculations. Neither has empirical derivation yielded reliable pair potentials, for these are frequently of short range and are fitted to experiniental data by assuming the non-pairwise higher-order terms to be negligible. The pseudopotential theory indicates that the former is a poor assumption, and there is both theoretical and experimental evidence that the latter is not strictly correct in the case of Al.The objective here is t o construct a pair potential for A1 by fitting a long-range function derived from pseudopotential theory to experimental phonon frequencies.It is known that phonon dispersion curves in aluminium are not in agreement with the central force model. This is an indication of non-pairwise multi-ion forces. A large l) Oulu, Finland. 6'