Hydrogen adsorption on metal surfaces

Extensive calculations of the ground state properties of hydrogen chemisorbed on transition metal surfaces are presented. The calculations are performed using the effective medium theory. The results for the chemisorption energies on all the 3d, 4d and 5d metals presented are in good agreement with experiment. The trends along a particular row are shown to be dominated by the degree of filling of the d band. The full adiabatic potential energy surface is presented for a number of experimentally interesting systems, including H/Ni(111), H/Ni(110), H/W(100) and H/W(110). Equilibrium sites, bond lengths, vibrational frequencies and surface diffusion energies are deduced and compared with experiment. Again, agreement is good. The surface and adsorbate parameters determining those observables are discussed. It is shown that a simple canonical relationship exists between the perpendicular vibrational frequency and the metal-hydrogen bond length. This formulation, which is not based on pair potentials, should be useful as a first estimate of bond lengths from measured vibrational data.     

Shape of the local-vibration band of adsorbed hydrogen-bonded molecular complexes

Within the framework of a dephasing model, a simple expression is obtained that describes a change in the shape of the vibrational band of the hydrogen atom upon adsorption of hydrogen-bonded complexes. The surface effect is taken into account by introducing the parameter of removal of the degeneration of low-frequency libration modes. As a coupling of the complex with the surface increases, the width of the spectral band and shift of its maximum decrease, and their ratio increases from 1.38 to 2.45.     

Storage of Entangled States with Multiple Trapped Ions in Thermal Motion

This paper presents an alternative scheme to realize the storage of entangled states for multiple trapped ions including W state, Bell states, and GHZ states even with ions which exchange vibrational energy with a heating surrounding. Our scheme requires that the ions be simultaneously excited by two laser beams with different frequencies.In this scheme the vibrational degrees of freedom are only regarded as intermediate states and the ions exchange energy via the mediation of the vibration of the vibrational mode in coupling processes. The scheme is insensitive to both the initial vibrational state and heating if the system remains in the Lamb-Dicke regime. Since the effective Rabi frequency has a small dependence on the vibrational quantum number the heating will have no direct effect on the internal state evolution.     

Bandshapes in polymer spectra

The shape of the vibrational envelope of an absorption band in the solution spectrum of a helical polymer is related to the shape of the corresponding band in the monomer. The approximation used is expected to be valid in both the strong and weak coupling limits. In the strong coupling limit it is shown that under certain conditions the polymer band consists of an extremely narrow peak shifted from the monomer line, as has been observed in the spectra of some cyanine dyes. The identification of this peak with absorption by a propagating exciton mode is supported by a calculation of the effective distance of excitation transfer as a function of coupling strength.     

T1u×hg Jahn-Teller系统：D3d势阱中的频率分解与能级分裂

在C60分子中，未被填充的最低电子态具有T1u对称性，因此，对中性的C60而言，不论是通过分子内部激发，或是外部掺杂，都易被一个电子占据而形成Jahn-Teller（JT）活跃电子态.此态与五重简并的hg声子态耦合，构成所谓的T1u-hg -JT系统.在这一JT系统中，当只考虑电声的线性耦合时，其绝热势能面是一个槽形.但在实际的系统中，二阶电声耦合是存在的，理论研究表明，原来的势槽将被这二阶非线性耦合弯曲成D3d或D5d对称性的势阱.声子振动态在阱中将显示各向异性效应，使得声子沿不同的方向有不同的振动频率，进而影响势阱中的能级分布、势阱间的重叠积分，以及整个系统的隧道能级分裂等.对D3d势阱中各向异性效应进行了研究，利用幺正平移、?pik Pryce和标度变换等方法计算了系统势阱中的能级，以及阱中的振动频率，研究了势阱中的能级间隔以及微绕修正能量的变化，并由此导出了这些物理量在仅有线性耦合的势槽中变化的情形. 关键词： C60 Jahn-Teller效应 各向异性 电声耦合     

Vibrational energy transfer in a protein molecule

Mode coupling in a protein molecule was studied by a molecular dynamics simulation of the intramolecular vibrational energy transfer in myoglobin at near zero temperature. It was found that the vibrational energy is transferred from a given normal mode to a very few number of selective normal modes. These modes are selected by the relation between their frequencies, like Fermi resonance, governed by the third order mode coupling term. It was also confirmed that the coupling coefficients had high correlation with how much the coupled modes geometrically overlapped with each other.     

Role of Mode-mode Coupling in Short-time Excited State Decay

Master equation of a relevant electronic and vibrational system is derived for a special diabatic basis corresponding to vertical processes. It is shown that bath modes contribute dynamically to the inter-state coupling only at short times. For long times the bath-induced inter-state coupling is static and increases with the contribution of bath modes to the Stokes shift and to the Herzberg-Teller correction of the excited state. Simultaneously, the time evolution of excited state population is studied numerically for the system consisting of two electronic levels interacting with two vibrational modes, coupled to a heat bath. A mutual coupling of the vibrational modes in the excited state is taken into account (Duschinsky effect). Excited state population relaxes faster if interacting vibrational mode dissipates its energy via vibrational mode of a smaller eigenfrequency. Fast component of excited state depopulation cannot be achieved via coherent mode-mode coupling, if the second mode is not directly coupled to the electronic inter-state transition.     

T1uhg Jahn-Teller系统中的频率约化矩阵

在研究C₆₀的电声相互作用中,最重要的应是T_1u电子态与h_{g< /sub>振动模式的偶合,俗称作T1uhg Jahn-Teller(JT)系统.线 性的T1uhg JT系统的势能面上只有势槽的存在,而当非线性耦合 项加入后,势能面将被扭曲成具有Ｄ3d或Ｄ5d对称性的势阱.在振 动频率的各向同性假设下,势阱中h 关键词： 60分子')" href="#">Ｃ60分子 “杨-太勒”系统 ?pik-Pryce方法}     

Complex quasiparticle band structure induced by electron-phonon interaction: band splitting in the 1x1H/W110 surface

We show that the self-consistent solution of the complex Dyson equation for the electron-phonon (EP) problem introduces many body effects which are often observed in photoemission experiments. The formalism is applied to the H covered W(110) surface, using first-principles results for the electronic and vibrational structure. We demonstrate that the measured spin-polarized surface band splitting [Phys. Rev. Lett. 84, 2925 (2000)10.1103/PhysRevLett.84.2925; 89, 216802 (2002)] can be traced back to different quasiparticle (QP) states induced by EP coupling. Despite the breakdown of the single QP picture, the spectral functions are very well represented by the predicted multiple QP structure.     

On the stability of the polaron in one dimensional disordered systems

A one-dimensional disordered system of electrons described by a tight binding model interacting with vibrational degrees of freedom (in harmonic approximation) is considered. A stable configuration is determined by a numerical minimization of the total energy which is based on the adiabatic approximation. The behaviour of the electron density (charge density wave) and the density of states is analysed. The localization properties are investigated as well. In contrast to the corresponding disordered system with vanishing electron-phonon coupling the present model has an energy gap. The formation of the gap and the polaron band is shown to be quite different for both onsite and intersite types of coupling terms. For large disorder, the lattice distortion and the gap disappear if only the vibrational contribution to the intersite coupling is important. They increase, however, if only the vibrational contribution to the site energies is taken into account. In both cases the localization length decreases upon increasing the electron-phonon coupling energy. The results are discussed with respect to low dimensional organic materials and amorphous semiconductors.     

Electron-phonon interaction at the Si(111)-7 x 7 surface

It is shown that electron-phonon interaction provides a natural explanation for the unusual band dispersion of the metallic surface states at the Si(111)-(7 x 7) surface. Angle-resolved photoemission reveals a discontinuity of the adatom band at a binding energy close to the dominant surface phonon mode at h(omega0) = 70 meV. This mode has been assigned to adatom vibrations by molecular dynamics calculations. A calculation of the spectral function for electron-phonon interaction with this well-defined Einstein mode matches the data. Two independent determinations of the electron-phonon coupling parameter from the band dispersion and from the temperature-dependent phonon broadening yield similar values of lambda = 1.09 and lambda = 1.06.     

Si(111)理想、弛豫及2×1重构表面的声子谱研究

本文利用微扰的方法考虑了占据态与空态间的耦合对能带能量的影响,给出延展键轨道近似下半导体力常数的解析表达式.利用这些表达式求出Si(111)的理想、1×1弛豫及2×1Haneman模型重构表面的声子色散曲线及其表面振动的振幅分布.不同表面结果的比较显示弛豫及重构对表面声子性质具有决定性的影响.同时,分析表明Haneman的2×1表面重构模型不足以满意地解释有关实验结果.     

Interpretation of the IR spectral intensity anomaly of HCN by potential energy surface bifurcation along a normal mode

Stable normal IR modes vibrate in a convex basin of the potential energy surface (PES). The change to locally concave equipotential lines in a higher energy normal mode direction is interpreted as a possible reason for irreversible and rotation controlled internal vibrational energy redistribution (IVR) during excitation of that normal mode. In hydrogen cyanide (HCN) such an IVR process already occurs in the CN fundamental μ₁. The concept is proven by an explanation of the spectroscopic data: The disturbed IR absorption, the very high intensity in the neighbouring Q-branch of the bending overtone 3v¹₂, the emerging of only higher J lines in the R branch of μ₁, the intensity anomaly in the further state (1, 1¹, 0), and the nearly normal behaviour of the DCN μ₁ band.     

Phonon softening in metallic nanotubes by a Peierls-like mechanism

The radial dependency of the vibrational frequencies of single-wall carbon nanotubes in the G band (1500-1600 cm(-1)) is studied by density functional theory. In metallic nanotubes, a mode with A1 symmetry is found to be significantly softer than the corresponding mode in insulating tubes or graphite. The mechanism that leads to the mode softening is explored. It is reminiscent of the driving force inducing Peierls distortions. At ambient temperature, the energy gained by opening the gap is, however, not sufficient for a static lattice distortion. Instead the corresponding vibrational frequency is lowered.     

Electronic origin of the surface reconstruction and relaxation of the (001) surface of Mo and W

The reconstruction and the relaxation of the (001) surface of Mo and W are studied by using the tight-binding d band and the Born-Mayer repulsive potential. The d band parameters are set to reproduce band energies of ab initio band calculations at high symmetry points in the Brillouin zone and the parameters in the Born-Mayer potential are chosen to obtain the correct equilibrium lattice constant and the bulk modulus of the bulk crystal. First, we give a detailed discussion on the mechanism of the surface relaxation, and then show that the (001) surfaces of Mo and W are unstable to the c(2 × 2) mode but stable with regard to the (2 × 1) mode. By calculating the energy change up to the fourth order of atomic displacement, we determine the stable surface atomic structure which is in fair agreement with experiments.     

Surface vibrations on clean and hydrogen saturated W(100)

Electron energy loss Spectroscopy (EELS) and lattice dynamical calculations are used to investigate the vibrational properties of surface phonons and adsorbate phonons on clean and hydrogen-saturated W(100). Two distinct intrinsic surface vibrations are observed in specular scattering geometry. One of the surface modes is attributed to a surface resonance of a bulk longitudinal phonon at the hydrogen-stabilized (1×1) surface. The second surface mode occurs only on the low-temperature-stabilized c(2×2) [011] displacement surface. Detailed experimental studies and lattice dynamical analysis of the hydrogen-saturated W(100) surface account for a new hydrogen-derived loss peak at 118 meV in terms of an optic mode of the adsorbed layer. Experimental evidence of impact scattering resonances under certain kinematic conditions are observed.     

A DFT investigation of potential energy surface and vibrational properties of hydrogen adsorbed on the Rh(1 1 1) surface

Vibrational properties of hydrogen on the Rh(1 1 1) surface have been investigated theoretically. The potential energy surface for this system has been calculated within the density functional theory. The potential is found to be very anharmonic. The wave functions and their energies for the hydrogen motion on the potential energy surface (PES) have been calculated and assigned by using discrete variable representation. It was found that the vibrational wave function is localized at hollow site in the ground state for hydrogen on Rh(1 1 1). Higher excited states are of delocalized nature and mixed parallel and perpendicular character. Our results are in good agreement with the observed vibrational spectra of hydrogen on the Rh(1 1 1) surface.     

Rotational-vibrational band structure in 155Sm

The nuclear structure of ¹⁵⁵Sm has been studied via primary and secondary γ-rays and by internal conversion electrons following thermal neutron capture. Furthermore average resonance neutron capture spectra for various neutron energy ranges were recorded. A detailed level scheme with a complete set of levels with spin < $\text{7}\text{2}$ has been well established up to 1400 keV excitation energy. The neutron binding energy has been determined to be 5807.2(3) keV. The scheme is interpreted in a basis of Coriolis and ΔN = 2 coupled Nilsson states and compared with the less deformed Sm isotopes. A possible additional band coupling via the octupole vibrational mode is discussed.     

Vibronic coupling to nearly localized modes in diamond

The presence of sharp low energy vibronic progressions in several luminescing bands of brown diamonds is interpreted as due to a nearly localized vibrational mode, showing a weak coupling to resonant lattice phonons. The effect of this mode on the vibronic coupling is discussed and compared with experimental data.     

Quantum states of hydrogen transfer and vibration in malonaldehyde

New ab initio results on the 21D potential energy surface of malonaldehyde and a quantum mechanical treatment of the hydrogen transfer motion and its interaction with all vibrations are presented. An explicit approximate reaction path, close to the minimum energy path but matching the reactive normal mode near equilibrium, allows one to predict the ground state tunnelling frequency even when using small basis sets. With a barrier of 1144 cm^?1 (3.27kcal mol-¹) the tunnelling splitting is predicted to be 22.0cm^?1 for the parent species and 3.8 cm^?1 for the species deuterated in the hydrogen bond, in good agreement with the observed values 21.6 and 2.9 cm^?1, respectively. Predicted energy levels for excited states of the hydrogen transfer motion and for the non-reactive vibrations suggest a re-examination of the vibrational spectra and an extension of the number of vibrational factors in the basis set to improve the results for the vibrationally excited states.