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Phases with the composition K2MgSi5O12, belonging to the leucite structure group were synthesised under dry and hydrothermal conditions and studied using 29Si NMR. The 29Si spectrum for the dry-crystallised material (which is cubic) consists of a single broad line, suggesting a high degree of disorder. The hydrothermally crystallised material (which is probably monoclinic, with a distorted leucite lattice) has a 29Si spectrum which consists of ten lines of equal intensity, two of which have small chemical shift anisotropies and are therefore assigned to Q4(4Si) sites. These data have been interpreted in terms of a structure with 12 distinct tetrahedral sites over which 2 Mg atoms and 10 Si atoms are fully ordered. A 2-dimensional COSY spectrum shows correlations between some Q4(3Si) silicon atoms and two other Q4(3Si) silicon atoms. This fully constrains the topology of the unit cell. Two schemes of Si/Mg ordering over the unit cell can give good fits to the COSY spectrum. Using the tetrahedral (T) site notation defined for natural tetragonal leucite, the first of these arrangements involves Mg and Q4(4Si) silicon atoms each occupying one T1-type site and one T3-type site, and Q4(3Si) silicons occupying the remaining sites, i.e. four T2-type sites, two T1-type sites and two T3-type sites. In the second arrangement, the T2-type sites are occupied by Mg atoms and Q4(4Si) silicon atoms and all the T1-and T3-type sites are occupied by Q4(3Si) atoms.

In this study, the adsorption of Flutamide (FLT) anticancer drug on the Zn doped single-walled carbon nanotube (5, 5) (SWCNT-Zn (5, 5)) has been investigated. This study has been performed in the gaseous phase and in water and ethanol solvents phases, in the basis and excited states, using density functional theory (DFT) and molecular orbitals (MO) calculation methods. DFT calculations performed at B3LYP quantum chemical level abs at 6-311G (d, p) basis set. Firstly, the structure of FLT was optimized at B3LYP/6-311G (d,p) theoretical level. The obtained results clearly demonstrate the energy stability of the optimized geometries and obviously show that the nature of Flutamide adsorption energy on the surface of SWCNT is in the range of the physisorption. Afterwards, the various structures of SWCNT (5, 5) and the adsorption of FLT on the outer surface of SWCNT (5, 5) was investigated using DFT method. The energies of FLT, SWCNT (5, 5), Zn doped SWCNT (5, 5), HOMO and LUMO orbitals, gap energy and dipole moments were calculated using DFT and MO methods.

Infrared absorption spectra of the high-pressure phases of cristobalite and their coordination numbers of silicon atoms

Energies of different conformers of 22 amino acid molecules and their protonated and deprotonated species were calculated by some density functional theory (DFT; SVWN, B3LYP, B3PW91, MPWB1K, BHandHLYP) and wave function theory (WFT; HF, MP2) methods with the 6-311++G(d,p) basis set to obtain the relative conformer energies, vertical electron detachment energies, deprotonation energies, and proton affinities. Taking the CCSD/6-311++G(d,p) results as the references, the performances of the tested DFT and WFT methods for amino acids with various intramolecular hydrogen bonds were determined. The BHandHLYP method was the best overall performer among the tested DFT methods, and its accuracy was even better than that of the more expensive MP2 method. The computational dependencies of the five DFT methods and the HF and MP2 methods on the basis sets were further examined with the 6-31G(d,p), 6-311++G(d,p), aug-cc-pVDZ, 6-311++G(2df,p), and aug-cc-pVTZ basis sets. The differences between the small and large basis set results have decreased quickly for the hybrid generalized gradient approximation (GGA) methods. The basis set convergence of the MP2 results has been, however, very slow. Considering both the cost and the accuracy, the BHandHLYP functional with the 6-311++G(d,p) basis set is the best choice for the amino acid systems that are rich in hydrogen bonds.

The lowest singlet–triplet gap in CCl 2, CBr 2 and CI 2

Extensive ab initio study of the electronic states of CP radical including spin–orbit coupling

Ab initio and density functional theory studies of the potential energy surface of the LiNC → LiCN isomerization

Repulsive interatomic potentials calculated using Hartree-Fock and density-functional theory methods

For the first time, the structures and energies for the hydrogen bonding of a 1:1 complex formed between formamide and methanol molecules have been computed with various pure and hybrid density functional theory (DFT) and ab initio methods at varied basis set levels from 6‐31g to 6‐31+g(d,p). Five reasonable geometries on the potential energy surface of methanol and formamide system are considered and their relative stability is discussed. The infrared (IR) spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. From the systematic studies, it is found that all the DFT methods selected here correctly compute the dimerization energies and geometries, with the B3P86 method predicting the hydrogen bond lengths relatively shorter and BPW91 yielding the interaction energies relatively lower. Finally, the solvent effects on the geometries of the formamide–methanol complexes have also been investigated using self‐consistent reaction field (SCRF) calculations with five different DFT methods at the 6‐31+g(d,p) basis set level. The results indicate that the polarity of the solvent has played an important role on the structures and relative stabilities of different isomers. Moreover, the basis set superposition error correction is critical to the interaction energies in the polar solvents. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Phenolic compounds generally has special smell, are easily soluble in water, organic solvents (alcohols, esters, chloroform, ethyl acetate), and in aqueous solutions of bases, and are colorless or colorful, crystalline and amorphous materials. Phenols form colorful complexes when they form compounds with heavy metals. In this study, the structural properties of a compound formed by pyrocatechines and iron is investigated theoretically.The optimized geometric parameters (bond lengths, bond and dihedral angles), conformational analysis, normal mode frequencies and corresponding vibrational assignments of the compound are theoretically examined by means of B3LYP hybrid density functional theory (DFT) method together with 6-31+g(d,p) and Cep-121g basis sets. All the calculations were performed by using Gaussian 09.A1 program and GaussView 5.0.8 was used for visualization of the structure and simulated vibrational spectra.Sum of electronic and zero-point energies of the compound is calculated as -2407.935 a.u. The geometrical parameters calculated from DFT method with the basis set of 6-31+g(d,p) of the compound: The bond lengths of the compound are calculated as C-H (1,09 A), C-O (1,29 A), C-C(1,43 A), O-Fe(1,90 A), respectively. The angles of the compound is find out as O-Fe-O (90,11°), C-O-Fe(112,81°), C-C-O(120,06°), C-C-C (119,61°), C-C-H (120,78°), respectively. C-O vibration frequencies (frequency values are scaled by 0.9648) of the compound are calculated in the range of 1296-1473. The most intense vibrations of O-C are symmetric frequency at 1360 cm-1 and asymmetric at 1473 cm-1 frequency. C=C aromatic ring vibrations are calculated at 1340 and 1569 cm-1. C-H aliphatic vibrations are calculated in the range of 3077 and 3107 cm-1. O-Fe vibrations are observed as stretch and twist in the range of 506-571 cm-1.

Nuclear magnetic resonance, vibrational spectroscopic studies, physico-chemical properties and computational calculations on (nitrophenyl) octahydroquinolindiones by DFT method

Vibrational spectra (FT-IR, FT-Raman), frontier molecular orbital, first hyperpolarizability, NBO analysis and thermodynamics properties of Piroxicam by HF and DFT methods

Molecular design of cage phosphine oxides (6-phospha-1,3,9,12-tetrasila-bicyclo[4.4.4]tetradecan-6-oxides) with four Si-containing acceptor fragments and one P=O donor fragment was performed using density functional theory methods (B3PW91 and ωB97X-D). Substituents at the silicon and phosphorus atoms were selected to favor the existence of the structures in the endo form containing a P=O···Si interaction. The competition of four silicon atoms for bonding to the phosphoryl oxygen atom was used to assess the coordinating ability of the phosphoryl group and to determine the nature of the P=O bond in phosphine oxides.

Bond dissociation energies in organometallic compounds

Efficient optical resolution of 2-(4-chlorophenoxy)propanoic acid with lipase by the use of organosilicon compounds as substrate: the role of silicon atom in enzymatic recognition