title: An ab initio density functional study of the optical functions of 9-Methyl-3-Thiophen-2-YI-Thieno [3,2e] [1,2,4] Thriazolo [4,3c] Pyrimidine-8-Carboxylic Acid Ethyl Ester crystals.
abstract: An ab initio investigation of the optical constants of 9-Methyl-3-Thiophen-2-YI-Thieno [3,2e] [1,2,4] Thriazolo [4,3c] Pyrimidine-8-Carboxylic Acid Ethyl Ester crystal is performed within a framework of local density approximation (LDA), and the Engel-Vosko generalized gradient approximation (EV-GGA) exchange correlation potentials. It is established that there are two independent molecules (A and B) exhibiting different intra-molecular interactions: C-H⋯O (A) and C-H⋯N (B). These intra-molecular interactions favor stabilization of the crystal structure for molecules A and B. It should be emphasized that there exist remarkable π-π interactions between the pyrimidine rings of the two neighbors B molecules giving extra strengths and stabilizations to the superamolecular structure. These different intra-molecular interactions C-H⋯O (A) and C-H⋯N (B) and the π-π interaction between the pyrimidine rings of the two neighbors B molecules give principal contribution to dispersion of optical properties. With a view to seek deeper insight into the electronic structure, the optical properties were investigated. Our calculations show that the optical constants are very anisotropic. The EVGGA calculation shows a blue spectral shift of around 0.024 eV with significant changes in the spectra compared to the LDA calculation. The observed spectral shifts are in agreement with the calculated band structure and corresponding electron density of states.
authors.affiliation: School of Complex Systems, FFWP - South Bohemia University, Nove Hrady 37333, Czech Republic. maalidph@yahoo.co.uk
authors.forename: Ali H
authors.initials: AH
authors.lastname: Reshak
authors.forename: I V
authors.initials: IV
authors.lastname: Kityk
authors.forename: R
authors.initials: R
authors.lastname: Khenata
authors.forename: Y
authors.initials: Y
authors.lastname: Al-Douri
authors.forename: S
authors.initials: S
authors.lastname: Auluck
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D055620:Optical Phenomena; D011743:Pyrimidines / Q000737:chemistry*; D011789:Quantum Theory; D013844:Thiazoles / Q000737:chemistry*
chemical_list: C575579:9-methyl-3-thiophen-2-YI-thieno(3,2e)(1,2,4)thriazolo(4,pc) Pyrimidine-8-carboxylic acid ethyl ester; D011743:Pyrimidines; D013844:Thiazoles