Search results for "molecular clusters"
showing 10 items of 868 documents
Instability of cuboctahedral copper clusters.
1992
Equilibrium structures of copper clusters up to 10 000 atoms are studied using molecular-dynamics and effective-medium theory. Icosahedral closed-shell clusters are most stable up to \ensuremath{\sim}2500 atoms and the Wulff polyhedra are favored for larger clusters. Cuboctahedral closed-shell clusters up to \ensuremath{\sim}2000 atoms are unstable. They undergo a nondiffusive transition to an icosahedral structure at low temperatures and melt directly above the fcc-cluster-melting temperature. The melting temperature decreases with decreasing cluster size but not as deeply as has been reported for pure metals.
The accuracy of molecular dipole moments in standard electronic structure calculations
2000
Abstract A systematic investigation has been carried out of the accuracy of calculated molecular equilibrium dipole moments of 11 polar closed-shell molecules, using the HF, MP2, CCSD and CCSD(T) models and correlation-consistent basis sets. Augmented basis sets are important for improving the basis-set convergence, but the quality of the results depends more on the correlation treatment than on the cardinal number of the basis set. Augmented triple-zeta basis sets are sufficient for most calculations. The mean absolute error of the HF calculations is 0.16 D, which is reduced at the MP2 and CCSD levels to 0.048 and 0.025 D, respectively. The CCSD(T) errors are small – typically
An ab initio potential energy surface for the C2H2-N2 system
2012
International audience; An ab initio potential energy surface determined at the CCSD(T) level of theory is presented for the van der Waals complex C2H2-N2. Additional calculations performed with the HF- and DFT-SAPT methods compare well with the CCSD(T) results and allow a better understanding of the main features of this interaction potential surface. An expansion of this surface over spherical harmonics has also been performed. The global energy minimum of the complex is obtained for the linear conformation. The T conformations are the least attractive. Such characteristics mainly arise because of the variation, in sign and in absolute value of the electrostatic energy between all these c…
Dipole Moments and the Direction of the Transition Dipole Moment of Some Intramolecular Exciplexes
1988
The dipole moments of some intramolecular exciplex systems have been determined from the effect of an electric field on their fluorescence and are compared to those estimated from solvent shift measurements. The charge transfer between the donor and acceptor subunits is between 0.6 and 0.9 of a full charge transfer. The face-to-face type exciplexes show considerable deviations from the general behaviour what might be due to some admixture of locally excited configurations to the exciplex wave function, in this way reducing the dipole moment values and changing the direction of the transition dipole moment.
Aza-BODIPY: A New Vector for Enhanced Theranostic Boron Neutron Capture Therapy Applications
2020
Boron neutron capture therapy (BNCT) is a radiotherapeutic modality based on the nuclear capture of slow neutrons by stable 10B atoms followed by charged particle emission that inducing extensive damage on a very localized level (<
Potential models for the simulation of methane adsorption on graphene: development and CCSD(T) benchmarks
2018
Different force fields for the graphene–CH4 system are proposed including pseudo-atom and full atomistic models. Furthermore, different charge schemes are tested to evaluate the electrostatic interaction for the CH4 dimer. The interaction parameters are optimized by fitting to interaction energies at the DFT level, which were themselves benchmarked against CCSD(T) calculations. The potentials obtained with both the pseudo-atom and full atomistic approaches describe accurately enough the average interaction in the methane dimer as well as in the graphene–methane system. Moreover, the atom–atom potentials also correctly provide the energies associated with different orientations of the molecu…
Proton-neutron pairing correlations in the self-conjugate nucleus 42Sc
2021
Collinear laser spectroscopy of the N=Z=21 self-conjugate nucleus 42Sc has been performed at the JYFL IGISOL IV facility in order to determine the change in nuclear mean-square charge radius between the Iπ=0+ ground state and the Iπ=7+ isomer via the measurement of the 42g,42mSc isomer shift. New multi-configurational Dirac-Fock calculations for the atomic mass shift and field shift factors have enabled a recalibration of the charge radii of the 42−46Sc isotopes which were measured previously. While consistent with the treatment of proton-neutron, proton-proton and neutron-neutron pairing on an equal footing, the reduction in size for the isomer is observed to be of a significantly larger m…
Shaping of a ground state rotational wavepacket by frequency-chirped pulses
2001
0953-4075; A coherent rotational superposition state is produced in the ground vibronic level of N2 through the interaction of the molecule with the electric field vector of a nonresonant laser pulse. This rotational wavepacket is shaped with a linear frequency chirp of the laser field. The structural shape of the rotational coherences shows a strong dependence with the frequency-chirp amplitude. A comparison with a theoretical model allows the interpretation of the observed effects in terms of dephasing of the wavepacket induced by the laser phase distortion. Application of the presented results to the phase characterization of short XUV pulses is suggested.
Temperature concepts for small, isolated systems: 1/t decay and radiative cooling
2003
We report on progress in our investigations of cluster cooling. The analysis of measurements is based on introduction of the microcanonical temperature and a statistical description of the decay of an ensemble with a broad distribution in temperature. The resulting time dependence of the decay rate is a power law close to t �1 , replaced by nearly exponential decay after a characteristic time for quenching by radiative cooling. We focus on results obtained for fullerenes, both anions and cations and recently also neutral C60.
Cavitation of electron bubbles in liquid parahydrogen
2011
Within a finite-temperature density functional approach, we have investigated the structure of electron bubbles in liquid parahydrogen below the saturated vapour pressure, determining the critical pressure at which electron bubbles explode as a function of temperature. The electron-parahydrogen interaction has been modelled by a Hartree-type local potential fitted to the experimental value of the conduction band-edge for a delocalized electron in pH(2). We have found that the pressure for bubble explosion is, in absolute value, about a factor of two smaller than that of the homogeneous cavitation pressure in the liquid. Comparison with the results obtained within the capillary model shows t…