Search results for " quantum chemistry"
showing 10 items of 549 documents
N -Diphenylmethyl-2-propenamide: theoretical study of the structure and interaction with a DNA model system
2001
Abstract N -diphenylmethyl-2-propenamide (NDP) was synthesised and characterised. Pharmacological in vitro tests pointed out that NDP had a cytotoxic activity on a human ovarian carcinoma comparable to that of doxorubicin. Hypothesising that this in vitro cytotoxic activity could be mainly due to intercalating interactions, between the drug and DNA fragments, ab initio calculations, at the Hartree–Fock (HF) level, were performed on the structure, and on the conformational properties of NDP, whereas its interaction with an (AC)(TG) dinucleotide triphosphate duplex (DD) was studied by the ONIOM method, at HF and PM3 level for NDP and DD, respectively. The supposed intercalation process with t…
Theoretical study of the effect of substituent and backbone conformation on the electronic properties of symmetrically substituted poly(di‐n‐alkylsil…
1994
We present the results of ab initio 3‐21G∗ geometry optimizations and valence effective Hamiltonian (VEH) band structure calculations aimed at determining the evolution of the geometric and electronic (ionization potential, electron affinities, and band gaps) properties of all‐trans poly(dimethylsilane), poly(diethylsilane), poly(di‐n‐propylsilane), and poly(di‐n‐butylsilane) when increasing the size of the alkyl group. In the latter polymer, we have also studied the 7/3 conformation, in order to analyze the effect of the backbone conformation on the geometric and electronic structure. The VEH ionization potentials of all‐trans poly(di‐n‐alkylsilanes) are almost equal, and as experimental p…
Photoelectrical properties of thin films of DMABI derivatives
2011
Organic thin films with semiconducting properties have been intensively studied in nowadays due to very promising applications in organic electronics, for example, organic photovoltaic. Among organic semiconductors, group of indandiones with their photoelectrical properties, thermal and chemical stability are good candidates for use in design of novel molecular electronic devices. We have investigated photoconductivity quantum efficiency and its spectral dependence of two dimetilaminobenzylidene-1,3-indandione derivatives. Values of the photoconductivity threshold energy and optical energy gap are obtained. These results are compared with calculated transfer energy gap estimated according t…
Measurement of the first ionization potential of astatine by laser ionization spectroscopy
2013
The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of the minute quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV. New ab initio calculations are performed to sup…
Ab initio study of phase competition in (La1−c,Src)CoO3 solid solutions
2013
Abstract (La 1 − c ,Sr c )CoO 3 (LSC) solid solutions are promising materials for high temperature electrochemical cells and cathodes of solid oxide fuel cells. The Density Functional Theory (DFT) was applied to calculate the energies of the different superstructures in LSC which are stable with respect to formation of anti-phase domains. The energy parameters determining the relative stability of the cubic superstructures (phases) are extracted from these calculations. Using the Concentration Wave formalism and the energy parameters for different phases from DFT calculations, the temperature dependences of the long-range order parameters were obtained characterizing the order–disorder tran…
From Pentalene to Dicyclopenta[b,g]naphthalene, or the Change towards Delocalized Structures
2005
Lining triples-corrected coupled-cluster methods as well as other high-level theoretical approximations, the optimized parameters and isomerization barriers of the family of compounds cyclopentadiene-(benzene) x -cyclopentadiene (x 0, 1, 2) are computed. In contrast to previous studies, s-indacene presents a localized C 2 h geometry. Also, the localized structure of pentalene is found to be the most stable, but when two benzene rings are intercalated between the five-member rings of pentalene, the resulting molecule preferably adopts a delocalized D 2 h conformation.
Ab-initio Calculation of the Properties of Permalloys Used in Electrical Machines
2006
In this paper an ab-initio calculation that allows to describe the main features of permalloys is presented. The calculation is bawd on Korringa-Kohn-Rostoker electronic structure method. The dependence of the magnetocryttalline anisotropy and of the magnetostriction on the concentration of non magnetic addiction is computed.
Pbca-Type In2O3: The High-Pressure Post-Corundum phase at Room Temperature.
2014
High-pressure powder X-ray diffraction and Raman scattering measurements in cubic bixbyite-type indium oxide (c-In2O3) have been performed at room temperature. On increasing pressure c-In2O3 undergoes a transition to the Rh2O3-II structure but on decreasing pressure Rh2O3-II-type In2O3 undergoes a transition to a previously unknown phase with Pbca space group which is isostructural to Rh2O3-III. On further decrease of pressure, we observed a phase transition to the metastable corundum-type In2O3 near room conditions. Recompression of the metastable corundum-type In2O3 at room temperature leads to a transition to the Rh2O3-III phase, thus showing that the Rh2O3-III phase is the post-corundum…
Phase Stability of Lanthanum Orthovanadate at High Pressure
2016
The journal of physical chemistry / C 120(25), 13749 - 13762(2016). doi:10.1021/acs.jpcc.6b04782
Semi-empirical calculations of the Nb-ion positions in doped crystals
1998
The atomic and electronic structures of Nb impurities in doped perovskite KTaO3 crystals are calculated using the semi-empirical quantum chemical method of the intermediate neglect of the differential overlap (INDO) and a supercell model. When seven Ta ions are replaced by seven Nb ions, the latter clearly demonstrate self-ordering effects which are related to the experimentally observed impurity-induced phase transition. A single Nb impurity reveals an off-centre displacement which is very close to that found in XAFS experiments. The relevant energy gain is very small, approximately 0.0375 eV, which is much smaller than the Nb-clustering energy gain (0.12 eV). These results led us to the c…