Journal of Chemical Physics
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Image effects in transport at metal-molecule interfaces We present a method for incorporating image-charge effects into the description of charge transport through molecular devices. A simple model allows us to calculate the adjustment of the transport levels, due to the polarization of the electrodes as charge is added to and removed from the molecule. For this, we use the charge distributions of the molecule between two metal electrodes in several charge states, rather than in gas phase, as obtained from a density-functional theory-based transport code. This enables us to efficiently model level shifts and gap renormalization caused by image-charge effects, which are essential for understanding molecular transport experiments. We apply the method to benzene di-amine molecules and compare our results with the standard approach based on gas phase charges. Finally, we give a detailed account of the application of our approach to porphyrin-derivative devices recently studied experimentally by Perrin et al. [Nat. Nanotechnol. 8, 282 (2013)], which demonstrates the importance of accounting for image-charge effects when modeling transport through molecular junctions.
Journal of Chemical Physics - Tập 143 Số 17 - 2015
<i>Ab initio</i> study on the ground and low-lying excited states of cesium iodide (CsI) Potential energy curves (PECs) for the ground and low-lying excited states of the cesium iodide (CsI) molecule have been calculated using the internally contracted multireference configuration interaction calculation with single and double excitation method with the relativistic pseudopotentials. PECs for seven Λ-S states, XΣ+1, 2Σ+1, Σ+3, Π1, and Π3 are first calculated and then those for 13 Ω states are obtained by diagonalizing the matrix of the electronic Hamiltonian Ĥel plus the effective one-electron spin-orbit (SO) Hamiltonian ĤSO. Spectroscopic constants for the calculated ground X0+-state PEC with the Davidson correction are found to agree well with the experiment. Transition dipole moments (TDMs) between X0+ and the other Ω states are also obtained and the TDM between X0+ and A0+ is predicted to be the largest and that between X0+ and B0+ is the second largest around the equilibrium internuclear distance. The TDMs between X0+ and the Ω=1 states are estimated to be nonzero, but they are notably small as compared with those between the 0+ states. Finally, vibrational levels of the X0+ PEC for the two isotopic analogs, Cs133I and Cs135I, are numerically obtained to investigate the isotope effect on the vibrational-level shift. It has been found that the maximized available isotope shift is ∼30cm−1 around v=136.
Journal of Chemical Physics - Tập 128 Số 2 - 2008
Bonding and potential energy curves for NiH and NiH2 The MINDO/SR procedure does well in reproducing experimental observations and theoretical ab initio calculated properties of NiH and NiH2. The occupied Ni d orbitals are nonbonding and remain lower in energy than the bonding Ni s and p orbitals in both NiH and NiH2. In agreement with experiment the lowest state of NiH2 is calculated to be a triplet with σ and δ holes in the d orbitals. A number of bent metastable states of NiH2 have been found, with the geometry being influenced indirectly by the d-orbital occupancy. One triplet state with a triangular geometry can be readily formed from H2 plus Ni and is stable by 9 kcal/mol with respect to dissociation into Ni plus H2. The H–H bond is stretched and reduced in energy but is not broken. This is a highly activated H2 molecule but there is still a large activation evergy, 42 kcal/mol, to completely break the H–H bond.
Journal of Chemical Physics - Tập 80 Số 5 - Trang 2042-2048 - 1984
Addition of Symmetrical Diatomic Molecules to Benzene The reaction of hydrogen and benzene to form 1,2-dihydrobenzene is considered, and the activation energy of the reaction is calculated with various assumptions concerning directed valence. It is shown that one may calculate approximate heats of reactions by considering exchange integrals only between electrons on neighboring atoms in a molecule, but this is not possible in calculating activation energies. The hydrogenation of benzene is considered as an eight electron problem, and the system serves to illustrate the degree of simplification of the secular equation arising from the symmetry of the system. The matrix elements of the factored equation are calculated. Activation energies of the reactions involved in the adsorption of H2 and C6H6 on Ni have been calculated and lead one to expect that the reaction might be achieved more easily catalytically.
Journal of Chemical Physics - Tập 3 Số 1 - Trang 49-55 - 1935
Fourier transform emission spectroscopy of the jet-cooled CCN free radical The à 2Δ–X̃ 2Π electronic transition of the CCN free radical was observed in emission with a high-resolution Fourier transform spectrometer. The CCN was jet-cooled in a corona-excited supersonic jet expansion of diazoacetonitrile (HC(N2)CN) in helium. From the 000–000, 000–001, 000–002, and 000–100 vibronic bands spectroscopic constants were derived including the ground-state vibrational frequencies, ν3=1050.7636(6), 2ν3=2094.8157(18), and ν1=1923.2547(69) cm−1.
Journal of Chemical Physics - Tập 92 Số 4 - Trang 2244-2247 - 1990
Rotational analysis of the 0 band of the <i>A</i>̃ 3<i>E</i>–<i>X</i>̃ 3<i>A</i>2 system of methylnitrene The optical emission spectrum of the methylnitrene radical has been observed at a resolution of 0.07 cm−1. Transitions to subbands with K up to 3 in the X̃ 3A2 ground state were observed and a full rotational analysis carried out. Comparison of the structural information with the highest level theoretical calculations shows agreement to within the estimated error.
Journal of Chemical Physics - Tập 96 Số 2 - Trang 919-926 - 1992
The laboratory microwave spectrum of the cyanide radical in its <i>X</i> 2Σ+ ground state The microwave absorption spectrum of the CN molecule in the v=0 and v=1 vibrational states of the electronic ground state has been obtained in glow discharges in nitrogen–cyanogen mixtures at room temperature. Zeeman modulation is used for detection of the signal, and the microwave source is phase locked and digitally programmed by a computer. For each vibrational state the frequencies of the seven strongest hyperfine components of the N=0→1 rotational transition have been extracted from a careful regression analysis of the complex line shapes observed in the digitized spectral data. For the v=0 state the resulting rest frequencies and molecular parameters are in good agreement with, but more precise and accurate than, the values obtained from earlier radioastronomical studies. For the excited vibrational state the present work provides the first determination of the hyperfine parameters. The precision of the results for both states is sufficient to give a reliable measure of the variation of the spin–rotation constant (γ) and the hyperfine constants (b, c, and eQq) with vibrational quantum number.
Journal of Chemical Physics - Tập 67 Số 9 - Trang 3956-3964 - 1977
Extension of the CN Red and Violet Band Systems The wavelengths and intensity distributions for the red (A 2Π→X 2Σ) and violet (B 2Σ→X 2Σ) bands which were observed in a mixture of active nitrogen and CH4 are given. Bands which originate in the A 2Π and B 2Σ states with excitation energies in the range 4.5-6 eV are well developed. The wavelength range studied was 3000-6700 Å. About 20 of the violet bands and 30 of the red bands have not been reported previously.
Journal of Chemical Physics - Tập 48 Số 5 - Trang 1980-1984 - 1968
Fluctuation of the number of adsorbed particles analyzed by a virial expansion: Comparison between experiment and theory The irreversible random adsorption of particles on a surface is guided by the available surface function φ. The relative fluctuation σ2/〈n〉 in the number of particles n in a finite region provides one characterization of the distribution of these particles on the surface. We show rigorously that the two quantities are given by the same expression to first order in the surface coverage, for any irreversible adsorption process. This is confirmed in two particular cases: for random sequential adsorption, where values for σ2/〈n〉 from numerical simulations can be compared to an analytic expression for φ, and for Ballistic deposition, where experimental values for deposition under a strong gravitational influence can also be compared to an existing analytical expression for φ.
Journal of Chemical Physics - Tập 102 Số 12 - Trang 5077-5081 - 1995
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