Dynamical and static dipole polarizability of metal clusters studied within different density functional approximations

Issue title: Computational aspects of electric polarizability calculations: Atoms, Molecules and clusters Part II

Article type: Research Article

Authors: Torres, M.B.^a | Balbás, L.C.^{b; *}

Affiliations: [a] Departamento de Matemáticas y Computación. Universidad de Burgos, E-09006 Burgos, Spain | [b] Departamento de Física Teórica. Universidad de Valladolid, E-47011 Valladolid, Spain

Correspondence: [*] Corresponding author. E-mail: balbas@lcb.fam.cie.uva.es.

Abstract: We study the linear response of pure and doped metal clusters to spin-dependent and spin-independent external fields within the framework of the time-dependent density functional theory. As test cases we have considered the response of clusters with spin-saturated configurations (Na9+, Na8, Na21+, Na20, Na40, Na4Pb and Na6Pb) and with spin-polarized configurations (Na6+, Na5Pb, Al11Fe, Al18 and Al18Fe). For spin-dependent excitations we have obtained in all the pure and doped sodium clusters a strongly collective spin mode of surface type lying at lower energies than the unperturbed particle-hole excitations. This mode uncouples cleanly from the electric dipole mode in the case of spin-saturated clusters, but for spin-polarized clusters these two modes turn out to be intertwined in the responses to spin-dependent and to spin-independent fields. We have performed the calculations within two different exchange-correlation potentials, the first constructed from the local density approximation by Perdew and Wang and the second constructed by Parr and Ghosh starting from the strongly non-local Amaldi Approximation. The latter incorporates the correct −1/r long-range behaviour leading to calculated static polarizabilities and photoabsorption spectra closer to experiments that the results from local density calculations. For the doped clusters NanPn and AlnFe we have compared the results obtained within two descriptions of the atoms surrounding the central impurity atom, namely the jellium model and the spherical average of the pseudopotentials method. The polarizabilities of AlnFe clusters with n⩽18, calculated within the two ionic models are similar and for n>9 are also similar to those of pure Aln clusters. The main difference between jellium and pseudopotential models when describing doped AlnFe clusters is obtained for the dipole response at several tens of eV for certain sizes where the last occupied d orbital has different occupation number in the pseudopotential model than in the jellium model.

Keywords: Metal clusters, photoabsorption spectrum, exchange-correlation functional

DOI: 10.3233/JCM-2004-4401

Journal: Journal of Computational Methods in Sciences and Engineering, vol. 4, no. 4, pp. 517-549, 2004