Atomistic simulation of phonon dispersion for body-centred cubic alkali metals

Abstract

Atomistic simulations of phonon dispersion for body-centred cubic alkali metals were carried out using the modified analytic embedded atom potentials. The expressions for atomic force constants are derived, the cohesive energy and elastic constants are calculated, and the phonon dispersion curves of Li, Na, K, Rb, and Cs are calculated along five principal symmetry directions. The calculated results are in good agreement with the available experiments. For all of the five alkali metals, in the same direction, a similar phonon dispersion curve is obtained in spite of the successive phonon frequency decreases for Li, Na, K, Rb, and Cs, which may be related to the atom mass increases or the cohesive energy decreases.

An embedded-atom-method model for alkali-metal vibrations

“…The MAEAM model discussed by Hu and Masahiro (HM) produces results similar to the those of the CM model [33]. Zhang and coworkers have published two sets of dispersion curves based on the MAEAM approach; overall, the degree of agreement with experiment is comparable to that of the JO-model calculated curves displayed in figure 1 [34,35].…”

Force and Elastic Constants of Metals and Alloys

“…Results of these researches are identical and given in [42] using a modified built-in analytical potential, which will be coordinated with experiment [41] more badly than elastic constants, calculated in [17,18]. The authors [42] didn't specify a calculation method for elastic constants, but they used the BornKarman's force constants. The Table 8 shows that the calculation results [17,18] of elastic constants C 11 , C 12 , C 44 for Na, K, Rb and Cs are close to the corresponding results [12] and is consistent with experimental data [43][44][45][46].…”

“…Formulas (30) for BCC metals and general formulas were approved in [17,18] on an example of alkaline metals Li, Na, K, Rb and Cs by means of calculations of elastic constants with use of the Ashkroft's model potential [39,40]. Results of these researches are identical and given in [42] using a modified built-in analytical potential, which will be coordinated with experiment [41] more badly than elastic constants, calculated in [17,18]. The authors [42] didn't specify a calculation method for elastic constants, but they used the BornKarman's force constants.…”

Vibrational dynamics within the embedded-atom-method formalism and the relationship to Born–von-Kármán force constants

“…We note an extension to embedded-atom method presented here, known as the modified analytic EAM (MAEAM), has been used to calculate vibrational properties of alkali and noble metals. [8][9][10][11][12] Originally introduced to account for the negative Cauchy pressure in Cr, the key feature of the MAEAM is an additional energy term that depends upon the square of the atomic charge density. 13 However, as the MAEAM does not appear to possess any advantage for describing vibrational structure, we shall not consider it further.…”