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Analytic expression of thermodynamic quantities for molecular cryocrystals of nitrogen type with fcc and hcp structures in harmonic, classical and anharmonic approximations

The analytic expressions of thermodynamic quantities such as the Helmholtz free energy, the internal energy, the entropy, the molar heat capacity at constant volume for molecular cryocrystals of N2 type with face-centered cubic (FCC) and hexagonal close-packed (HCP) structures in harmonic, classical and anharmonic approximations are obtained by combining the statistical moment method (SMM) and the self-consistent field method (SCFM). | JOURNAL OF SCIENCE OF HNUE DOI 10.18173 2354-1059.2015-0038 Mathematical and Physical Sci. 2015 Vol. 60 No. 7 pp. 94-103 This paper is available online at http stdb.hnue.edu.vn ANALYTIC EXPRESSION OF THERMODYNAMIC QUANTITIES FOR MOLECULAR CRYOCRYSTALS OF NITROGEN TYPE WITH FCC AND HCP STRUCTURES IN HARMONIC CLASSICAL AND ANHARMONIC APPROXIMATIONS Nguyen Quang Hoc1 Mai Thi La1 Vo Minh Tien2 and Dao Kha Son2 1 Faculty of Physics Hanoi National University of Education 2 Facultyof Physics Tay Nguyen University Abstract. The analytic expressions of thermodynamic quantities such as the Helmholtz free energy the internal energy the entropy the molar heat capacity at constant volume for molecular cryocrystals of N2 type with face-centered cubic FCC and hexagonal close-packed HCP structures in harmonic classical and anharmonic approximations are obtained by combining the statistical moment method SMM and the self-consistent field method SCFM . Keywords Statistical moment method self-consistent field method cryocrystal. 1. Introduction Molecular crystals comprising a vast and comparatively little investigated class of solids are characterized by a diversity of properties. Up to now only solidified noble gases have systematically been investigated and this is due to the availability of relevant theoretical models and the ease of comparing theories with experimental results. Recently experimental data have been obtained for simple non-monoatomic molecular crystals as well and this in turn has stimulated the appearance of several theoretical papers on that subject. This paper deals with the analysis of thermodynamic properties of the group of non-monoatomic molecular crystals including solid N2 and CO that have similar physical properties. These crystals are formed by linear molecules and in their ordered phase the molecular centers of mass are situated at the site of a face-centered cubic FCC pattern the molecular axes being directed to the four spatial diagonals of a cube .