1066-3622/03/4503-0237$25.00 2003 MAIK Nauka/Interperiodica Radiochemistry, Vol. 45, No. 3, 2003, pp. 237 242. Translated from Radiokhimiya, Vol. 45, No. 3, 2003, pp. 217 222. Original Russian Text Copyright 2003 by Plekhanov, German, Sekine. Electronic Structure of Technetium Metal, Calculated in the Approximation of the X -Discrete Variation Method 1 Yu. V. Plekhanov*, K. E. German*, and R. Sekine** * Institute of Physical Chemistry, Russian Academy of Sciences, Moscow, Russia ** Shizuoka University, Shizuoka, Japan Received December 26, 2002 Abstract Electronic structure of the fragments (number of atoms from 6 to 93) of hexagonal close-packed and face-centered cubic structures of technetium metal was calculated in the approximation of the X -discrete variation nonempirical method. The results agree well with band calculations of both occupied and unoccu- pied electronic states in solid Tc as well as with the experimental data of conversion electron and optical spectroscopy. The quantum chemical model can be used for calculations of technetium ruthenium binary phases which can be formed in the course of transmutation of technetium metal. The electronic structure of technetium metal was extensively studied in the 1970 1980s (see references in [1, 2]). However, modern works on transmutation of technetium metal into ruthenium and studies of properties of Tc Ru binary systems [3 6] make this problem urgent again. The results of almost all theoretical calculations, which were based on band methods, could not be compared with experimental data on the electronic structure owing to the lack of such data at that time [1, 7]. Some physical properties of solids were predicted on the basis of the band cal- culations. However, chemical properties are mainly due to local interactions and are described more cor- rectly by cluster molecular models [2]. In addition, the cluster approach allows simulation of both ideal crystal and defective structures or multicomponent systems (alloys and solid solutions). Our previous work was limited by the possibilities of the X -scattered wave procedure. In this paper, the electronic structure of a greater number of ap- preciably larger models was calculated by more rigor- ous X -discrete variation procedure [9]. The calcula- tions were performed by DVSCAT program [10] in the full electronic basis of numerical orbitals using 1s 5p atomic functions of Tc. Electron exchange was accounted for by the Slater procedure with the param- eter of 0.7. The individual contributions of the atomic orbitals were estimated by the Mulliken population analysis. Technetium metal mainly crystallizes in a hexagon- al closed-packed lattice (hcp) with the parameters a = 2.7409 0.0035 and c = 4.3987 0.0034 [11]. Each 1 Reported at the Third Russian Japanese Seminar on Techne- tium (Dubna, June 23 July 1, 2002). technetium atom is surrounded by twelve nearest neighbors. Six of them are at a distance of 0.2735 nm, and the other six atoms, at a distance of 0.2704 nm. In polycrystalline technetium films thinner than 15 nm, a face-centered cubic (fcc) modification stable at room temperature was found (a = 0.368 nm, mini- mal Tc Tc distance 0.26 nm) [12]. Technetium nano- particles supported by oxide matrices also have a cubic lattice [13]. Bulk metal is a weak paramagnetic passing into superconducting state at relatively high temperature, T c = 8.24 K. The critical temperature of thin films is lower: T c = 4.9 K. In [14, 15], sub- stoichiometric technetium carbide TcC 1 x (x > 0.8) is considered as virtual modification of technetium metal stabilized with the carbon impurity. However, the features of formation of technetium carbide with 17% carbon content and the narrow range of existence of the nonstoichiometric carbides suggest formation of a compound like Tc 6 C. Although this phase un- doubtedly exhibits metallic properties (in particular, conductivity), we will not consider it in this work and will focus our attention on pure technetium metal. As in our pervious work [8], we considered model structures of hcp and fcc lattices (Fig. 1). All model clusters were constructed by consecutive increase in the number of spherical layers of atoms around the center. The main hcp modification was simulated by clusters with occupied and unoccupied center. The validity of the main results of our calculation can be confirmed by comparing some parameters of the electronic structure of the clusters, presented in the table and in Figs. 2 8, with the known experimental [1, 7, 11 13] and theoretical [1 2, 8] data. As seen from Fig. 2 and 4, the shape of the spec-