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Parrinello Molecular Dynamics Simulations (parrinello + molecular_dynamics_simulation)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Short-Range Structure of Yttrium Alumino-Silicate Glass for Cancer Radiotherapy: Car,Parrinello Molecular Dynamics Simulations,

ADVANCED ENGINEERING MATERIALS, Issue 7 2010
Jamieson K. Christie
We present Car,Parrinello molecular dynamics (CPMD) simulations of yttrium alumino-silicate (YAS) glass. Alumino-silicate glass microspheres are used as vectors of yttrium radioisotopes in cancer radiotherapy; understanding in detail how yttrium is bound within the glass network is important to control the unwanted release of radioactive yttrium in the bloodstream. Our simulations, focused on a specific composition relevant to practical applications, show that silicon and aluminum form a disordered glass network, where Si is mainly four-coordinated, whereas, Al is mainly four- and five-coordinated. Yttrium cations have a network-modifying role, disrupting the alumino-silicate network by breaking Si(Al)O bonds and coordinating the resulting non-bridging oxygens (NBO). The local environment of yttrium in the glass turns out to be rather flexible: between five and eight oxygen atoms, with a marked predominance of NBO, are found coordinated to a central Y cation, leading to a corresponding broad and multimodal distribution of OYO angles. [source]

Car,Parrinello Molecular Dynamics Study of the Blue-Shifted F3CH,,,FCD3 System in Liquid N2

CHEMPHYSCHEM, Issue 6 2006
Pawel Rodziewicz Dr.
Abstract Fluoroform, as confirmed by both experimental and theoretical studies, can participate in improper H-bond formation, which is characterized by a noticeable increase in the fundamental stretching frequency ,(CH) (so-called blue frequency shift), an irregular change of its integral intensity, and a CH bond contraction. A Car,Parrinello molecular dynamics simulation was performed for a complex formed by fluoroform (F3CH) and deuterated methyl fluoride (FCD3) in liquid nitrogen. Vibrational analysis based on the Fourier transform of the dipole moment autocorrelation function reproduces the blue shift of the fundamental stretching frequency ,(CH) and the decrease in the integral intensity. The dynamic contraction of the CH bond is also predicted. The stoichiometry of the solvated, blue-shifted complexes and their residence times are examined. [source]

Can Electrophilicity Act as a Measure of the Redox Potential of First-Row Transition Metal Ions?

CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2007
Jan Moens
Abstract Previous contributions concerning the computational approach to redox chemistry have made use of thermodynamic cycles and Car,Parrinello molecular dynamics simulations to obtain accurate redox potential values, whereas this article adopts a conceptual density functional theory (DFT) approach. Conceptual DFT descriptors have found widespread use in the study of thermodynamic and kinetic aspects of a variety of organic and inorganic reactions. However, redox reactions have not received much attention until now. In this contribution, we prove the usefulness of global and local electrophilicity descriptors for the prediction of the redox characteristics of first row transition metal ions (from Sc3+|Sc2+ to Cu3+|Cu2+) and introduce a scaled definition of the electrophilicity based on the number of electrons an electrophile ideally accepts. This scaled electrophilicity concept acts as a good quantitative estimate of the redox potential. We also identify the first solvation sphere together with the metal ion as the primary active region during the electron uptake process, whereas the second solvation sphere functions as a non-reactive continuum region. [source]

Thermal Effects and Vibrational Corrections to Transition Metal NMR Chemical Shifts

CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2004
Sonja Grigoleit Dr.
Abstract Both zero-point and classical thermal effects on the chemical shift of transition metals have been calculated at appropriate levels of density functional theory for a number of complexes of titanium, vanadium, manganese and iron. The zero-point effects were computed by applying a perturbational approach, whereas classical thermal effects were probed by Car,Parrinello molecular dynamics simulations. The systematic investigation shows that both procedures lead to a deshielding of the magnetic shielding constants evaluated at the GIAO-B3,LYP level, which in general also leads to a downfield shift in the relative chemical shifts, ,. The effect is small for the titanium and vanadium complexes, where it is typically on the order of a few dozen ppm, and is larger for the manganese and iron complexes, where it can amount to several hundred ppm. Zero-point corrections are usually smaller than the classical thermal effect. The pronounced downfield shift is due to the sensitivity of the shielding of the metal centre with regard to the metal,ligand bond length, which increase upon vibrational averaging. Both applied methods improve the accuracy of the chemical shifts in some cases, but not in general. [source]