Search results for "ELECTRONIC STRUCTURE"
showing 10 items of 722 documents
Interpretation of unexpected behavior of infrared absorption spectra ofScF3beyond the quasiharmonic approximation
2016
Scandium fluoride (${\mathrm{ScF}}_{3}$), having cubic ${\mathrm{ReO}}_{3}$-type structure, has attracted much scientific attention due to its rather strong negative thermal expansion (NTE) in the broad temperature range from 10 to 1100 K. Here we use the results of diffraction and extended x-ray absorption fine-structure (EXAFS) spectroscopy to interpret the influence of NTE on the temperature dependence of infrared absorption spectra of ${\mathrm{ScF}}_{3}$. Original infrared absorption and EXAFS experiments in a large temperature range are presented and interpreted using ab initio lattice dynamics simulations within and beyond quasiharmonic approximations. We demonstrate that ab initio e…
Second generation Car-Parrinello molecular dynamics
2014
Computer simulation methods, such as Monte Carlo or molecular dynamics, are very powerful theoretical techniques to provide detailed and essentially exact informations on rather complex classical many-body problems. With the advent of ab initio molecular dynamics (AIMD), where finite-temperature dynamical trajectories are generated using interatomic forces which are calculated on the fly using accurate electronic structure calculations, the scope of computational research has been greatly extended. This review is intended to outline the basic principles as well as being a survey of the field. Beginning with the derivation of Born–Oppenheimer molecular dynamics, the Car–Parrinello method and…
Symmetry and Electronic Structure of Noble Metal Nanoparticles and the Role of Relativity
2004
High resolution photoelectron spectra of cold mass selected Cu_n-, Ag_n- and Au_n- with n =53-58 have been measured at a photon energy of 6.42 eV. The observed electron density of states is not the expected simple electron shell structure, but seems to be strongly influenced by electron-lattice interactions. Only Cu55- and Ag55- exhibit highly degenerate states. This is a direct consequence of their icosahedral symmetry, as is confirmed by density functional theory calculations. Neighboring sizes exhibit perturbed electronic structures, as they are formed by removal or addition of atoms to the icosahedron and therefore have lower symmetries. Gold clusters in the same size range show complet…
Attosecond control of dissociative ionization of O2molecules
2011
We demonstrate that dissociative ionization of O(2) can be controlled by the relative delay between an attosecond pulse train (APT) and a copropagating infrared (IR) field. Our experiments reveal a dependence of both the branching ratios between a range of electronic states and the fragment angular distributions on the extreme ultraviolet (XUV) to IR time delay. The observations go beyond adiabatic propagation of dissociative wave packets on IR-induced quasistatic potential energy curves and are understood in terms of an IR-induced coupling between electronic states in the molecular ion.
Isotope shifts and hyperfine structure in the $\mathsf{ 3d ^2D_J \rightarrow 4p ^2P_J}$ transitions in calcium II
1998
The isotope shift and hyperfine structure in the three \(\) - transitions in Ca II have been studied by fast ion beam collinear laser spectroscopy for all stable Ca isotopes. The metastable 3d states were populated within the surface ionization source of a mass separator with a probability of about 0.1%. After resonant excitation to the 4p levels with diode laser light around 850 nm the uv photons from the \(\) transitions to the ground state were used for detection. Hyperfine structure parameters A and B for the odd isotope 43Ca, as evaluated from the splittings observed, agree well with theoretical predictions from relativistic many-body perturbation theory. Field shift constants \(\) and…
Star orbits in metal clusters
1993
A possibility that classical five-point star orbits play a dominant role for shell structures of large metal clusters is investigated quantum mechanically. With a soft Woods-Saxon spherical potential a signature of the five-point star orbit is found in the level densities. Quantum numbers of degenerate levels in the soft Woods-Saxon potential differ by 2 and 5 in radial nodes and angular momenta, respectively. Unlike the experimental observation the peaks in the mass spectrum are not equally spaced as a function of N 1/3 . The self-consistent jellium model does not reproduce the degeneracy associated with the five-point star orbits. It is demonstrated that by covering high-density metal clu…
In Silico Molecular Engineering of Dysprosocenium-Based Complexes to Decouple Spin Energy Levels from Molecular Vibrations
2019
Molecular nanomagnets hold great promise for spintronics and quantum technologies, provided that their spin memory can be preserved above liquid-nitrogen temperatures. In the past few years, the magnetic hysteresis records observed for two related dysprosocenium-type complexes have highlighted the potential of molecular engineering to decouple vibrational excitations from spin states and thereby enhance magnetic memory. Herein, we study the spin-vibrational coupling in [(CpiPr5)Dy(Cp*)]+ (CpiPr5 = pentaisopropylcyclopentadienyl, Cp* = pentamethylcyclopentadienyl), which currently holds the hysteresis record (80 K), by means of a computationally affordable methodology that combines first-pri…
Temperature-Dependent Change of the Electronic Structure in the Kondo Lattice System $YbRh_{2}Si_{2}$
2021
Seminar, Deutschland; Journal of physics / Condensed matter 00(00), 1-20 (2021). doi:10.1088/1361-648X/abe479
Plane-Wave Density Functional Theory
2016
Reduced scaling in electronic structure calculations using Cholesky decompositions
2003
The small numerical rank of the two-electron integral matrix for large molecular systems and large basis sets was demonstrated. Though, the current implementation still requires some improvements on the calculations done in the inner most loop of the decomposition do not exploit the parsity in the Cholesky vectors. With respect to the practical applicability of the presented method an efficient approach to geometrical derivatives was imperative. Such an approach was obtained including certain derivative product functions and decomposing an expanded integral matrix.