Finite-field method calculations. IV. Higher-order moments,dipole moment gradients,polarisability gradients and field-induced shifts in molecular properties: Application to N2, CO,CN−, HCN and HNC

In this paper, theoretical methods developed in III are applied in calculating polarisabilities, polarisability gradients and field-induced shifts, by the finite-field method. Values of dipole moment gradients and higher-order moments, calculated from the unperturbed wavefunctions, are also reported. Results for N₂, CO, CN^?, HCN and HNC have been obtained at the SCF level; some CI results for the N₂ polarisability components and moments and for the dipole moment gradients of HCN are also given. The calculated polarisability gradients and dipole moment gradients have been used to estimate the Raman scattering intensities and depolarisation ratios and the IR absorption intensities. Model calculations of field-induced shifts in bond length, vibrational levels, spectroscopic constants, force constants and dipole moment gradient are reported for N₂ and CO.The discrepancy between the SCF and experimental bond dipole moment gradients for HCN, previously noted in the literature, has been re-examined and resolved by our CI results.     

Ground-state inversion method applied to calculation of molecular photoionization cross-sections by atomic extrapolation: Interference effects at low energies

The ground-state inversion method, which we have previously developed for the calculation of atomic cross-sections [ 29 ], is applied to the calculation of molecular photoionization cross-sections. These are obtained as a weighted sum of atomic subshell cross-sections plus multi-centre interference terms. The atomic cross-sections are calculated directly for the atomic functions which when summed over centre and symmetry yield the molecular orbital wave function. The use of the ground-state inversion method for this allows the effect of the molecular environment on the atomic cross-sections to be calculated. Multi-centre terms are estimated on the basis of an effective plane-wave expression for this contribution to the total cross-section. Finally the method is applied to the range of photon energies from 0 to 44 eV where atomic extrapolation procedures have not previously been tested. Results obtained for H₂, N₂ and CO show good agreement with experiment, particularly when interference effects and effects of the molecular environment on the atomic cross-sections are included. The accuracy is very much better than that of previous plane-wave and orthogonalized plane-wave methods, and can stand comparison with that of recent more sophisticated approaches. It is a feature of the method that calculation of cross-sections either of atoms or of large molecules requires very little computer time, provided that good quality wave functions are available, and it is then of considerable potential practical interest for photoelectron spectroscopy.     

Sulfur ligand mediated electrochemistry of gold surfaces and nanoparticles: What,how, and why

Gold surfaces and gold nanoparticles are widely used. The surfaces and nanoparticles often have to be coated by sulfur-bound organic ligands, which both provide stability and participate in many desired processes. We overview here what, how, and why it is that the core Au-S surface bond offers such versatile structure and function.

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The Green's function density functional tight-binding (gDFTB) method for molecular electronic conduction

A review is presented of the nonequilibrium Green's function (NEGF) method "gDFTB" for evaluating elastic and inelastic conduction through single molecules employing the density functional tight-binding (DFTB) electronic structure method. This focuses on the possible advantages that DFTB implementations of NEGF have over conventional methods based on density functional theory, including not only the ability to treat large irregular metal-molecule junctions with high nonequilibrium thermal distributions but perhaps also the ability to treat dispersive forces, bond breakage, and open-shell systems and to avoid large band lineup errors. New results are presented indicating that DFTB provides a useful depiction of simple gold-thiol interactions. Symmetry is implemented in DFTB, and the advantages it brings in terms of large savings of computational resources with significant increase in numerical stability are described. The power of DFTB is then harnessed to allow the use of gDFTB as a real-time tool to discover the nature of the forces that control inelastic charge transport through molecules and the role of molecular symmetry in determining both elastic and inelastic transport. Future directions for the development of the method are discussed.     

FTIR光谱法研究天花粉蛋白的热去折叠过程

本文利用ＦＴＩＲ光谱技术和计算机辅助解析技术（二阶导数、去卷积和曲线拟合）研究了天花粉蛋白的热诱导去折叠过程。结果表明：在２５～８５℃温度范围内,天花粉蛋白的热去折叠是一个不可逆的分子间聚集的过程;二级结构随温度的变化暗示了折叠中间体的存在。     

An ab initio SCF calculation of the dipole-moment derivatives and infrared-absorption intensities of the water-dimer molecule

The dipole-moment derivatives and infrared-absorption intensities of the water dimer including several deuterated species have been calculated using ab initio SCF techniques. The results are compared with the analogous, quantities for monomeric water. In addition to the highly enhanced intensity of the intramolecular OH stretch most intermolecular modes that occur in the 90–600 cm^?1 region are also found to be very intense. An electrostatic model for the water dimer has been explored with a view to developing a possible scheme for the calculation of infrared intensities of larger clusters. As a result of the significant exchange and charge-transfer effects such a model is found to be unreliable in describing the dipole-moment derivatives that directly involve the hydrogen bond.     

Intermixed Adatom and Surface‐Bound Adsorbates in Regular Self‐Assembled Monolayers of Racemic 2‐Butanethiol on Au(111)

In situ scanning tunneling microscopy combined with density functional theory molecular dynamics simulations reveal a complex structure for the self‐assembled monolayer (SAM) of racemic 2‐butanethiol on Au(111) in aqueous solution. Six adsorbate molecules occupy a (10×√3)R30° cell organized as two RSAuSR adatom‐bound motifs plus two RS species bound directly to face‐centered‐cubic and hexagonally close‐packed sites. This is the first time that these competing head‐group arrangements have been observed in the same ordered SAM. Such unusual packing is favored as it facilitates SAMs with anomalously high coverage (30 %), much larger than that for enantiomerically resolved 2‐butanethiol or secondary‐branched butanethiol (25 %) and near that for linear‐chain 1‐butanethiol (33 %).     

Inequivalent XPS binding energies in symmetrical delocalized mixed-valence complexes

It has previously been assumed that an ESCA measurement on a mixed-valence-e.g., M(II)-M(III) - compound which yields two peaks for an inner-shell M ionization at energies close to those measured for separate M(II) and M(III) ions provides direct evidence that the complex has an unsymmetrical (trapped-valence) ground state rather than one in which the electrons are symmetrically delocalized. This assumption is incorrect. A complex which has a symmetrical ground state will have two accessible unsymmetrical photoionized states owing to electron relaxation in the strong field of the core hole. For a range of values of binding energy differences and electron coupling parameters, the photoionized states will be very nearly localized and the peak separation for a complex with delocalized ground state will be close to that for isolated M(II) and M(III) ions. The appearance of two M binding energies is thus not in itself evidence for electronic ground-state asymmetry in a mixed-valence compound. A model is proposed from which quantitative predictions are made.