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Journal of Chemical Physics

Rangeen Salih, C C Matthai
We have carried out molecular dynamics simulations using NAMD to study the diffusivity of Na and Cl ions across a POPC lipid bilayer membrane. We show that an imbalance of positively and negatively charged ions on either side of the membrane leads to the diffusion of ions and water molecules. We considered the cases of both weak and very strong charge imbalance across the membrane. The diffusion coefficients of the ions have been determined from the mean square displacements of the particles as a function of time...
March 14, 2017: Journal of Chemical Physics
E Celasco, G Carraro, M Smerieri, L Savio, M Rocca, L Vattuone
Free standing graphene is chemically inert but, as recently demonstrated, CO chemisorption occurs at low crystal temperature on the single layer grown by ethene dehydrogenation on Ni(111). Such layer is inhomogeneous since different phases coexist, the relative abundance of which depends on the growth conditions. Here we show by X ray photoemission and high resolution electron energy loss spectroscopies that the attained CO coverage depends strongly on the relative weight of the different phases as well as on the concentration of carbon in the Ni subsurface region...
March 14, 2017: Journal of Chemical Physics
Vincenzo Barone, Ivo Cacelli, Alessandro Ferretti, Giacomo Prampolini
The calculation of the energy gap between the magnetic states of organic poly-radicals still represents a challenging playground for quantum chemistry, and high-level techniques are required to obtain accurate estimates. On these grounds, the aim of the present study is twofold. From the one side, it shows that, thanks to recent algorithmic and technical improvements, we are able to compute reliable quantum mechanical results for the systems of current fundamental and technological interest. From the other side, proper parameterization of a simple Hubbard Hamiltonian allows for a sound rationalization of magnetic gaps in terms of basic physical effects, unraveling the role played by electron delocalization, Coulomb repulsion, and effective exchange in tuning the magnetic character of the ground state...
March 14, 2017: Journal of Chemical Physics
Jeff Mountjoy, Michelle Todd, Nicholas J Mosey
The evaluation of exact exchange (EXX) is an important component of quantum chemical calculations performed with ab initio and hybrid density functional methods. While evaluating exact exchange is routine in molecular quantum chemical calculations performed with localized basis sets, the non-local nature of the exchange operator presents a major impediment to the efficient use of exact exchange in calculations that employ planewave basis sets. Non-orthogonal generalized Wannier functions (NGWFs) corresponding to planewave expansions of localized basis functions are an alternative form of basis set that can be used in quantum chemical calculations...
March 14, 2017: Journal of Chemical Physics
Stine T Olsen, Thorsten Hansen, Kurt V Mikkelsen
Electron transport through a molecule is often described in one of the two regimes: the coherent tunnelling regime or the Coulomb blockade regime. The twilight zone of the two regimes still possesses many unsolved questions. A theoretical analysis of the oligophenylenevinylene OPV3 experiments by Bjørnholm and co-workers is performed. The experiments showed how two OPV3 derivatives performed very differently despite the strong similarity of the molecular structure, hence the experimental data showed two different transport mechanisms...
March 14, 2017: Journal of Chemical Physics
Ján Škoviera, Pavel Neogrády, Florent Louis, Michal Pitoňák, Ivan Černušák
Correlated ab initio methods (CASPT2 and CCSD(T)) in conjunction with the ANO-RCC basis sets were used to calculate potential energy curves (PECs) of the ground, valence, and Rydberg electronic states of CsH with the inclusion of the scalar relativistic effects. The spectroscopic constants of bound states were calculated from the PECs and compared with previous theoretical and/or available experimental data. Absorption and emission spectra arising from the transition between X(1)Σ(+) and A(1)Σ(+) states were modelled using vibrational and rotational energy levels and corresponding nuclear wave functions obtained via the direct numerical integration of one-dimensional rovibrational Schrödinger equation in the CASPT2/ANO-RCC electronic potentials...
March 14, 2017: Journal of Chemical Physics
Paul M Zimmerman
The incremental expansion provides a polynomial scaling method for computing electronic correlation energies. This article details a new algorithm and implementation for the incremental expansion of full configuration interaction (FCI), called iFCI. By dividing the problem into n-body interaction terms, accurate correlation energies can be recovered at low n in a highly parallel computation. Additionally, relatively low-cost approximations are possible in iFCI by solving for each incremental energy to within a specified threshold...
March 14, 2017: Journal of Chemical Physics
M Stefanski, M Lukaszewicz, D Hreniak, W Strek
The laser induced white emission (LIWE) was observed from Eu(3+):Sr2CeO4 nanocrystals. The samples were obtained in form of powders by the modified sol-gel route. The structure and morphology of the phosphors were investigated by powder X-ray diffraction and transmission electron microscope techniques. The intense LIWE occurred under reduced pressure and focused beam of near infrared laser excitation. The power and pressure dependencies exhibit evident threshold character typical for the avalanche effect. The photoconductivity of the Eu(3+):Sr2CeO4 nanocrystals measured as a function of different powers of excitation source was analyzed...
March 14, 2017: Journal of Chemical Physics
Irini K Gavra, Alexandra N Pilidi, Athanassios A Tsekouras
Films of 1-butanol were vapor deposited under vacuum conditions at cryogenic temperatures on a polycrystalline platinum foil. Kelvin probe measurements showed the generation of a large negative voltage on the vacuum side of the film relative to its back side in contact with the platinum foil. Voltages across vapor deposited films, which are known to require molecules with an electric dipole moment, were confirmed to be proportional to the amount of gas deposited at a given temperature. Voltages of several hundreds of volts were recorded for films that were a few thousand monolayers thick...
March 14, 2017: Journal of Chemical Physics
Y Z Chua, R Zorn, O Holderer, J W P Schmelzer, C Schick, E Donth
The aim of this paper is to decide which of the two possible thermodynamic expressions for the cooperativity length in glass forming liquids is the correct one. In the derivation of these two expressions, the occurrence of temperature fluctuations in the considered nanoscale subsystems is either included or neglected. Consequently, our analysis gives also an answer to the widely discussed problem whether temperature fluctuations have to be generally accounted for in thermodynamics or not. To this end, the characteristic length-scales at equal times and temperatures for propylene glycol were determined independently from AC calorimetry in both the above specified ways and from quasielastic neutron scattering (QENS), and compared...
March 14, 2017: Journal of Chemical Physics
Tobias Schäfer, Benjamin Ramberger, Georg Kresse
We present a low-complexity algorithm to calculate the correlation energy of periodic systems in second-order Møller-Plesset (MP2) perturbation theory. In contrast to previous approximation-free MP2 codes, our implementation possesses a quartic scaling, O(N(4)), with respect to the system size N and offers an almost ideal parallelization efficiency. The general issue that the correlation energy converges slowly with the number of basis functions is eased by an internal basis set extrapolation. The key concept to reduce the scaling is to eliminate all summations over virtual orbitals which can be elegantly achieved in the Laplace transformed MP2 formulation using plane wave basis sets and fast Fourier transforms...
March 14, 2017: Journal of Chemical Physics
W van Megen, H J Schöpe
The cage effect is generally invoked when discussing the delay in the decay of time correlation functions of dense fluids. In an attempt to examine the role of caging more closely, we consider the spread of the displacement distributions of Brownian particles. These distributions are necessarily biased by the presence of neighbouring particles. Accommodation of this bias by those neighbours conserves the displacement distribution locally and presents a collective mechanism for exploring configuration space that is more efficient than the intrinsic Brownian motion...
March 14, 2017: Journal of Chemical Physics
S P Bierwirth, P Münzner, T A Knapp, C Gainaru, R Böhmer
Highly unusual linear-response spectra involving contributions from hydrogen-bonded supramolecular processes and from structural relaxations are found in 4-methyl-3-heptanol mixed with 2-ethyl-1-hexylbromide. Although the mean time scales of the underlying relaxations are separated by more than 3 decades, the overall spectra cannot be decomposed into a sum of these processes. This finding challenges the ubiquitous practice of disentangling susceptibility spectra of Debye liquids by adding suitable subspectra...
March 14, 2017: Journal of Chemical Physics
Marsha I Lester
No abstract text is available yet for this article.
March 14, 2017: Journal of Chemical Physics
S Rudinsky, A S Sanz, R Gauvin
The numerical analysis of the diffraction features rendered by transmission electron microscopy typically relies either on classical approximations (Monte Carlo simulations) or quantum paraxial tomography (the multislice method and any of its variants). Although numerically advantageous (relatively simple implementations and low computational costs), they involve important approximations and thus their range of applicability is limited. To overcome such limitations, an alternative, more general approach is proposed, based on an optimal combination of wave-packet propagation with the on-the-fly computation of associated Bohmian trajectories...
March 14, 2017: Journal of Chemical Physics
Hongyang Li, Wenjian Liu, Bingbing Suo
Both top-down and bottom-up localization schemes are proposed for constructing localized molecular orbitals (LMOs) of open-shell systems, via least change from fragments to molecule. The success of both schemes stems from (1) the primitive fragment LMOs that are local not only in space but also in energy and (2) the "conquer step" that allows arbitrary assignment of the unpaired electrons to fragments. Moreover, integral occupations are retained, so as to facilitate subsequent treatment of electron correlation and excitation...
March 14, 2017: Journal of Chemical Physics
Apostolos Kalemos
The nature of the chemical bond in BeO(0,-), BeOBe(+,0,-), and in their hydrogenated products HBeO(0,-), BeOH, HBeOH, BeOBeH(+,0,-), and HBeOBeH has been studied through single and multi reference correlation methods. In all these species, excited and ionized atomic states participate in a resonant way making chemically possible molecules that have been termed hypervalent and explain also the "incompatible" geometrical structure of some species.
March 14, 2017: Journal of Chemical Physics
Sungsool Wi, Robert Schurko, Lucio Frydman
Cross-polarization (CP) experiments employing frequency-swept radiofrequency (rf) pulses have been successfully used in static spin systems for obtaining broadband signal enhancements. These experiments have been recently extended to heteronuclear I, S = spin-1/2 nuclides under magic-angle spinning (MAS), by applying adiabatic inversion pulses along the S (low-γ) channel while simultaneously applying a conventional spin-locking pulse on the I-channel ((1)H). This study explores an extension of this adiabatic frequency sweep concept to quadrupolar nuclei, focusing on CP from (1)H (I = 1/2) to (2)H spins (S = 1) undergoing fast MAS (νr = 60 kHz)...
March 14, 2017: Journal of Chemical Physics
Michael P Ziemkiewicz, Christian Pluetzer, Michael Wojcik, Jérôme Loreau, Ad van der Avoird, David J Nesbitt
Vibrationally state selective overtone spectroscopy and dynamics of weakly bound Ne-H2O complexes (D0((para)) = 31.67 cm(-1), D0((ortho)) = 34.66 cm(-1)) are reported for the first time, based on near infrared excitation of van der Waals cluster bands correlating with vOH = 2 ← 0 overtone transitions (|02(-)⟩←|00(+)⟩ and |02(+)⟩←|00(+)⟩) out of the ortho (101) and para (000) internal rotor states of the H2O moiety. Quantum theoretical calculations for nuclear motion on a high level ab initio potential energy surface (CCSD(T)/VnZ-f12 (n = 3,4), corrected for basis set superposition error and extrapolated to the complete basis set limit) are employed for assignment of Σ←Σ,Π←Σ, and Σ←Π infrared bands in the overtone spectra, where Σ(K = 0) and Π (K = 1) represent approximate projections (K) of the body angular momentum along the Ne-H2O internuclear axis...
March 14, 2017: Journal of Chemical Physics
C Faust, J Jones, J Huennekens, R W Field
We present results from experimental studies of the 11(0(+)) and 12(0(+)) electronic states of the NaCs molecule. An optical-optical double resonance method is used to obtain Doppler-free excitation spectra. Selected data from the 11(0(+)) and 12(0(+)) high-lying electronic states are used to obtain Rydberg-Klein-Rees and Inverse Perturbation Approach potential energy curves. Interactions between these two electronic states are evident in the patterns observed in the bound-bound and bound-free fluorescence spectra...
March 14, 2017: Journal of Chemical Physics
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