Search results for "init"

Ab initio modeling of copper adhesion on regular BaTiO3(001) surfaces

2005

Ab initio calculations have been performed for copper adsorption on a regular, defect-free TiO"2- and BaO-terminated (001) surfaces of a cubic BaTiO"3, using a posteriori HF-CC method as implemented into the CRYSTAL-03 computer code. To clarify the nature of the interfacial bonding, we use slab models of the Cu/BaTiO"3(001) interfaces with different one-side substrate coverages, varied from 1/8 monolayer (ML) up to 1/2 ML, over both TiO"2- and BaO-terminated surfaces. TiO"2 termination has been found to be energetically more favorable for the adsorption of copper atoms. In agreement with previous experimental and theoretical data, our calculations indicate essential contribution of atomic p…

Ab initio modelling of Y-O cluster formation in γ-Fe lattice

2016

Ab initio modelling of Y and O impurity atoms as well as VFe vacancies in the fcc-Fe lattice is performed in order to calculate the interactions between these defects, which are important for understanding of nanoparticles’ formation within the oxide dispersed strengthened steels. Large scale parallel calculations based on plane-wave method realised in VASP computer code show that VFe vacancies considerably influence the binding between the impurity atoms. In this study, we present the results of performed calculations providing the detailed information about the binding energies between the defects, the changes of their effective charges as well as displacements of the substitute atoms rel…

ChemInform Abstract: Weak Interactions Between Trivalent Pnictogen Centers: Computational Analysis of Bonding in Dimers X3E···EX3(E: Pnictogen, X: Ha…

2009

The nature of weak interactions in dimers X3E···EX3 (E = N−Bi, X = F−I) was investigated by wave function and density functional theory (DFT)-based methods. Out of the 20 systems studied, 10 are found to be bound at the CP-MP2 and LMP2 levels of theory. Detailed partition of the interaction energy into different components revealed that dispersion is the primary force holding the dimers together but there also exists an important ionic component whose contribution increases with increasing halogen size. As expected, standard density functionals fail to describe bonding in the studied systems. However, the performance of DFT methods can be easily improved via empirical dispersion correction …

1H, 13C NMR spectral and single crystal structural studies of toxaphene congeners. Quantum chemical calculations for preferred conformers of 2,5-endo…

2005

Abstract The 1H and 13C NMR chemical shifts for six toxaphene congeners: 2-exo,3-endo,6-exo,8,9,10-hexachloro- (1), 2-exo,3-endo,5-exo,9,9,10,10-heptachloro- (2), 2-exo,3-endo,6-exo,8,9,10,10-heptachloro- (3), 2-exo,3-endo,5-exo,6-endo,8,9,10-heptachloro- (4), 2-exo,3-endo,5-exo,6-endo,8,9,9,10-octachlorobornane (5) and 2,5-endo,6-exo,8,9,9,10,10-octachloro-2-bornene (6) are reported. Their chemical shift assignments have been obtained by means of Pulsed Field Gradient (PFG) Double Quantum Filtered (DQF) 1H,1H correlation spectroscopy (COSY), PFG 1H,13C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG 1H,13C Heteronuclear Multiple Bond Correlation (HMBC) experiments. A single crystal…

Chlorodicyclopentadienyloxoniobium(V) complexes revisited: The origin of the asymmetry in the 1H- and 13C-NMR spectra, X-ray crystal structures and a…

2000

Abstract 1H- and 13C-NMR spectra of chlorodicyclopentadienyloxoniobium(V) complex I and its four 1,1′-dialkyl substituted derivatives II–V have been recorded and assigned based on DQF 1H,1H-COSY and PFG 1H,13C-HMQC and HMBC experiments. Non-equivalences of all cyclopentadienyl protons and carbons in II–V (as reflected by their different 1H- and 13C-NMR chemical shifts) are explained by synchronous and out-of-phase rotations of the substituted cyclopentadienyl rings. A non-equivalence of the methyls in III (1,1′-di-isopropyl) is explained by a detailed inspection of the rotamers of the isopropyl groups. The X-ray structural data show that III and IV (1-methyl-1′-tert-butyl) crystallize in th…

Comparison of epimeric methyl lithocholate and methyl iso-lithocholate molecules: single crystal X-ray structure of methyl lithocholate, ab initio HF…

2003

Abstract 13 C NMR chemical shifts have been measured and assigned for epimeric methyl 3α/β-hydroxy-5β-cholan-24-oates (methyl lithocholate [3α-OH epimer] and methyl iso-lithocholate [3β-OH epimer]). Their molecular dynamics simulations suggest that for both epimers there exists two predominant gas phase conformations, which have been further forwarded for ab initio/HF optimizations and DFT/GIAO based 13 C NMR chemical shift calculations. Excellent linear relationships have been observed between experimental and calculated 13 C NMR chemical shifts for both epimers. For methyl lithocholate (MeLC), the other minimum energy conformation equates very well with the single crystal X-ray structure …

Corrigendum to “Comparison of epimeric methyl lithocholate and methyl iso-lithocholate molecules: Single crystal X-ray structure of methyl lithochola…

2003

A MRCI PS and CASSCF study of the ground state MgO dissociation energy

1991

Abstract Ab initio calculations at CASSCF and MRCI PS levels are used to determine the dissociation energy for the X 1 Σ + state of MgO, which adiabatically dissociates to the ground state 1 S g of magnesium and to the excited 1 D g state of oxygen, as well as other spectroscopic parameters. Emphasis is placed upon the problem of properly selecting an adequate active space in CASSCF calculations and upon the improvements obtained in MRCI by selecting perturbatively the most important contributions to the total wavefunction and evaluating the remaining ones only by perturbational method. Through a procedure based on stabilizing the computed dissociation energy, values of 3.87 eV (MRCI PS) an…

Structural and Spectroscopic Properties of Mg−Bacteriochlorin and Methyl Bacteriochlorophyllidesa,b,g, andhStudied by Semiempirical, ab Initio, and D…

2004

Ab initio HF/6-31G* and density functional B3LYP/6-31G* methods have been used to calculate fully optimized structures of methyl bacteriochlorophyllides a, b, g, and h and magnesium-bacteriochlorin...

Orbital-controlled reactions catalysed by zeolites: Electrophilic alkylation of aromatics

1994

The role of orbital control in product selectivity during electrophilic aromatic alkylation catalysed by zeolites was studied both theoretically and experimentally. In order to discuss this, the alkylation of toluene and m-xylene by methanol was carried out on a series of large-pore zeolites (HY). The changes in the para to ortho ratio observed on changing the framework Si/Al ratio of the zeolites were related to ab initio molecular orbital calculations of the LUMO energy of structurally alike model clusters but containing different tetrahedral cations around the active site. The observed correlation is discussed in terms of the HSAB principle by taking into account the influence of the cat…