Noncentral forces and lattice vibration in transition metals. II: α-iron, chromium and tungsten

Singh, Vineeta; Kharoo, H. L.; Kumar, Mahendra; Hemkar, M. P.

doi:10.1007/bf02726743

Cited by 20 publications

References 36 publications

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Force fields in d-band metals

Matthai

Grout

March

2009

Int. J. Quantum Chem.

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In transition metals, the d shells lead to relatively hard cores compared with the simpler sp metals. Furthermore, there is some evidence that directional effects due to d orbitals increase through the sequence face-centered-cubic (fcc), hexagonal close-packed (hcp), and body-centered-cubic (bcc) structures. These features have led us to study the utility of density-independent central pair forces, plus a volume-dependent energy for the face-centered metals Ni and Pt, and the relation between force fields in the solid and liquid states. For Ni, there is a need to change the phase of the oscillatory pair potential extracted from the liquid structure factor to account for the elastic properties of the solid and the measured phonon dispersion relation. In the case of Pt, a potential is constructed which gives a fair representation of the measured phonon dispersion curves, and the corresponding liquid structure factor above the melting point has been calculated by molecular dynamics. There is fair accord with the measured structure factor for liquid Pt as determined by x-ray scattering. While the above results strongly demonstrate the usefulness of such a pair potential representation of the force field in the fcc solid metals, we have also studied evidence for bcc metals (a) from solid phonon dispersion relations already available in the literature and (b) especially from results for elastic constants, both second and third order, from experiment and from central pair force models. For Cr there is a rather clear pointer that directionality is an essential ingredient to be included in a realistic force field. Finally, melting curves under pressure have been studied and confirm the hardness of the core repulsion.

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