NUCLEI AND MESOSCOPIC PHYSICS: Workshop on Nuclei and Mesoscopic Physic ‐ WNMP 2007

How changing physical constants and violation of local position invariance may occur?
View Description Hide DescriptionLight scalar fields very naturally appear in modern cosmological models, affecting such parameters of Standard Model as electromagnetic fine structure constant α, dimensionless ratios of electron or quark mass to the QCD scale, Cosmological variations of these scalar fields should occur because of drastic changes of matter composition in Universe: the latest such event is rather recent (redshift ), from matter to dark energy domination. In a two‐brane model (we use as a pedagogical example) these modifications are due to changing distance to “the second brane”, a massive companion of “our brane”. Back from extra dimensions, massive bodies (stars or galaxies) can also affect physical constants. They have large scalar charge proportional to number of particles which produces a Coulomb‐like scalar field This leads to a variation of the fundamental constants proportional to the gravitational potential, e.g. We compare different manifestations of this effect, which is usually called violation of local position invariance. The strongest limits are obtained from the measurements of dependence of atomic frequencies on the distance from Sun (the distance varies due to the ellipticity of the Earth's orbit).

A Cluster Model of and
View Description Hide DescriptionSmall nuclei provide an ideal testing ground of few‐body theories. is particularly interesting in that it shows an extended particle distribution similar to a halo nucleus, is loosely bound, and is a Borromean system. We apply a fully antisymmetric model with correct projection into eigenstates of angular momentum. Binding energies, charge radii, matter radii, and were obtained for the and cigar configurations. The same configurations were used to obtain the same observables for Were were then able to calculate the value for the beta decay of

Equation of State and Pairing Gaps in Cold Atoms and Low‐Density Neutron Matter
View Description Hide DescriptionCold Atom experiments provide a direct experimental test of the properties of neutron matter at extremely low densities, as is expected to be found in the crusts of neutron stars. These systems are very unusual in that the pairing gap is of the order of the Fermi energy, rather than the very small fraction typical for superfluids or superconductors. We compare the equation of state and the pairing gaps in these systems.

Two‐component Bose gases under rotation
View Description Hide DescriptionWe examine the formation of vortices in a one‐ and two‐component gas of bosonic atoms in a harmonic trap that is set rotating. Both the mean‐field Gross‐Pitaevskii approach, and the numerical diagonalization method are employed. For a two‐component Bose gas, we show that beside the well‐known coreless vortices of single quantization, the interatomic interactions between the two species may lead to coreless vortices of multiple quantization. We furthermore comment on the geometries of the interlaced vortex patterns. In the limit of weak interactions, we finally demonstrate a number of exact results.

Cold atom ballistics by coherent control
View Description Hide DescriptionWe use the technique of Stimulated Raman adiabatic passage (STIRAP) to affect transport of ultracold atoms between two optical lattices in relative motion. We show, using Floquet analysis and degenerate perturbation theory, that the dynamics of atoms in a particular time‐dependent optical lattice system can be reduced to the 3‐level STIRAP model, allowing for a simple description of their coherent acceleration.

Nondynamic Correlation and Coupled‐Cluster Methods
View Description Hide DescriptionThe coupled‐cluster (CC) methods that are based on the exponential Ansatz for the wave operator proved to be extremely valuable in quantum chemical computations of the molecular electronic structure and represent nowadays most accurate and often used post‐Hartree‐Fock approaches that are capable to attain chemical accuracy for many molecular properties of interest. Nonetheless, while the widely exploited single‐reference (SR) CC approaches, such as the CCSD method accounting for one‐ and two‐body cluster amplitudes or its CCSD(T) version perturbatively corrected for three‐body clusters—all available in numerous software packages—are remarkably efficient in handling of dynamical correlation effects, their performance rapidly deteriorates in the presence of quasidegeneracy of the reference configuration when the nondynamic correlations become important. A possible, computationally affordable, remedy for this failure is the so‐called reduced multireference (RMR) CCSD method, as well as its triple‐corrected version RMR CCSD(T). These methods exploit the complementarity of the configuration interaction (CI) and CC approaches and represent the topic of this communication.

A compact spin‐free coupled‐cluster theory for open‐shell systems
View Description Hide DescriptionWe present in this Paper a brief account of a novel spin‐free compact coupled cluster (CC) theory for simple open‐shell configurations, e.g. doublet and biradicals, which are not necessarily single determinants. A new cluster Ansatz for the wave‐operator is introduced, in which the spin‐free cluster operators are either of the type of closed‐shell‐like n hole‐n particle excitations or contain valence excitations, which may involve exchange spectator scatterings. The cluster operators with exchange valence spectator scatterings and the pure valence excitation operators are allowed to contract among themselves through the spectator orbitals. The novelty of the Ansatz is in the choice of a suitable automorphic factor accompanying each composite of non‐commuting operators, ensuring that each such composite appears only once. This leads to CC equations which terminate exactly at the quartic power of the cluster amplitudes, reminiscent of the closed‐shell CC theory. As example applications, we compute the state energies of the ground state of OH and radicals with cc‐pVDZ basis set and assess the performance of the theory by comparing the results with the benchmark full CI results in the same basis set. The results show the power and the efficacy of the method.

Extrapolating Potential Energy Surfaces by Scaling Electron Correlation: Isomerization of Bicyclobutane to Butadiene
View Description Hide DescriptionThe recently proposed potential energy surface (PES) extrapolation scheme, which predicts smooth molecular PESs corresponding to larger basis sets from the relatively inexpensive calculations using smaller basis sets by scaling electron correlation energies [A.J.C. Varandas and P. Piecuch, Chem. Phys. Lett. 430,448 (2006)], is applied to the PESs associated with the conrotatory and disrotatory isomerization pathways of bicyclo[l.l.0]butane to buta‐l,3‐diene. The relevant electronic structure calculations are performed using the completely renormalized coupled‐cluster method with singly and doubly excited clusters, and a non‐iterative treatment of connected triply excited clusters, termed CR‐CC(2,3). A comparison with the explicit CR‐CC(2,3) calculations using the large correlation‐consistent basis set of the cc‐pVQZ quality shows that the cc‐pVQZ PESs obtained by the extrapolation from the smaller basis set calculations employing the cc‐pVDZ and cc‐pVTZ basis sets are practically identical, to within fractions of a millihartree, to the true cc‐pVQZ PESs. It is also demonstrated that one can use a similar extrapolation procedure to accurately predict the complete basis set (CBS) limits of the calculated PESs from the results of smaller basis set calculations at a fraction of the effort required by the conventional point‐wise CBS extrapolations.

Some Recent Developments of Quantum Monte Carlo to Molecular Systems.
View Description Hide DescriptionA brief review of recent advances in quantum Monte Carlo for the electronic structure of molecules at the University of California, Berkeley, is given based on an invited talk presented at the Workshop on Nuclear and Mesoscopic Physics.

Continuum shell model: From Ericson to conductance fluctuations
View Description Hide DescriptionWe discuss an approach for studying the properties of mesoscopic systems, where discrete and continuum parts of the spectrum are equally important. The approach can be applied (i) to stable heavy nuclei and complex atoms near the continuum threshold, (ii) to nuclei far from the region of nuclear stability, both of the regions being of great current interest, and (iii) to mesoscopic devices with interacting electrons. The goal is to develop a new consistent version of the continuum shell model that simultaneously takes into account strong interaction between fermions and coupling to the continuum. Main attention is paid to the formation of compound resonances, their statistical properties, and correlations of the cross sections. We study the Ericson fluctuations of overlapping resonances and show that the continuum shell model nicely describes universal properties of the conductance fluctuations.

Decay Rates Statistics of Unstable Classically Chaotic Systems
View Description Hide DescriptionDecay law of a complicated unstable state formed in a high energy collision is described by the Fourier transform K(t) of the two‐point correlation function of the scattering matrix. Although each constituent resonance state decays exponentially the decay of a state composed of a large number of such interfering resonances is not, generally, exponential. We introduce the decay rates distribution function by representing the decay law in the form of the mean‐weighted decay exponent In the framework of the random matrix approach we investigate the properties of the distribution function and its relation to the more conventional statistics of the decay widths. The latter is not in fact conclusive as concerns the evolution at the times shorter than the characteristic Heisenberg time. Exact analytical consideration is presented for the case of systems without time reversal symmetry.

Doorway States and the Super‐Radiant Mechanism
View Description Hide DescriptionA new approach to physics of doorway states in nuclear reactions is developed. It is argued that the coupling of intrinsic states to the continuum through special doorway state(s) may create the situation similar to the optical super‐radiance, when the segregation of broad (short‐lived) resonances and trapped (long‐lived) states occurs. Necessary conditions are discussed, along with applications to isobaric analog states, single‐particle resonances, giant resonances, and fission through a double‐humped barrier. This pattern can be observed in other mesoscopic systems as well.

Time‐dependent Green's functions approach to nuclear reactions
View Description Hide DescriptionNonequilibrium Green's functions represent underutilized means of studying evolution of quantum many‐body systems. In view of a rising computer power, an effort is underway to apply the Green's functions to the dynamics of central nuclear reactions. As the first step, mean‐field evolution for the density matrix for colliding slabs is studied in one dimension. Strategy to extend the dynamics to correlations is described.

Quantum Transport in Mesoscopic Semiconductor Devices: Vortices, Flows and Atomistic Effects
View Description Hide DescriptionExciting developments in nanometer scale semiconductor MOS technology are briefly reviewed. The physics of such devices may be understood by applying 2D and 3D non‐equilibrium Green function theory to their simulation. Although the current‐voltage characteristics show excellent transistor behaviour the underlying transport is strictly quantum mechanical. This will be illustrated by showing the self‐consistent energy resolved current flows and charge densities for typical target devices particularly double‐gate MOS devices and wrap‐round gate silicon nanowire MOS devices. The existence of quantized vortices even at very high temperature will be discussed and the effects of phase de‐coherence. Scattering processes are particularly interesting in such devices and many novel interference phenomena and atomistic scattering effects occur including polarisation effects arising from the close proximity of source and drain and gate regions. These small devices comprise in effect finite many‐body systems that are driven far from equilibrium. Each device has a different microscopic structure and environment at the atomic level and this leads to variability in the macroscopic device parameters. The full modelling of such systems is one of the major challenges to present day technology. At present the field is at a watershed where future modelling will require atomic level descriptions of the devices thus making contact with molecular electronics and novel media such as carbon nanotubes.

Self‐consistent Hartree‐Fock approximation for non‐equilibrium electron transport through nanostructures
View Description Hide DescriptionWe present the formulation of self‐consistent Hartree‐Fock theory for non‐equilibrium electron transport in nanostructures. The derivations are performed by our method for direct calculations of asymptotic, non‐equilibrium steady state averages. We use asymptotic single‐particle density matrix to approximate the molecular Hamiltonian by its Hartree‐Fock form. Then we obtain the close system of coupled nonlinear integral equations for the transformation matrix, which diagonalizes the Hartree‐Fock Hamiltonian, and asymptotic single particle density matrix.

Electron correlations and the conductance of a quantum point contact at finite temperature
View Description Hide DescriptionTo describe electron transport through a quantum point contact we formulate and solve a nonlocal kinetic equation for the density matrix of electrons. The electron‐electron interaction is treated by perturbation theory with account of higher order terms. At zero temperature, the approach results in the Landauer formula for conductance of a quantum point contact. At finite temperature, the leading correction to the current of correlated electrons scales as temperature squared. The corresponding correction to conductance G is negative and strongly enhanced in the region The effect may be relevant to the so called “0.7 structure” of conductance observed experimentally.

Scanning Charge Accumulation Probe of Semiconductor Donor Molecules
View Description Hide DescriptionWe have developed a scanning probe method that is able to detect individual electrons entering a system of semiconductor donor atoms. We have applied the method to a system of Si donors within a GaAs‐AlGaAs heterostructure sample. The data compare well to a model that considers donor molecules, effectively formed by nearest‐neighbor silicon atoms.

Electron Transport through Protein Fragments
View Description Hide DescriptionBy combining ab initio and semi‐empirical techniques, we construct a theoretical model of electron transport through oligopeptide molecules, i.e. short protein fragments. With no fitting parameters, this model achieves quantitatively accurate agreement with experiment, and so enables the extraction of chemical and physical information, such as bonding geometry and the behavior of the molecules under stretching, from experimental data. Furthermore, the model explains the experimentally observed current rectifying properties of these molecules as a consequence of the hybridization of interfacial states at opposite gold‐molecule contacts; under appropriate bias, these poorly conducting localized states mix to form well conducting whole‐molecule orbitals. Finally, we predict that oligopeptide molecules can be made to exhibit negative differential resistance by a related mechanism, thus opening the way to many interesting protein‐based nanoelectronic devices.

Photochemistry of Biological Chemosensors, Organic Light‐Emitting Diodes, and Inner‐shell Electronic Processes
View Description Hide DescriptionThe photochemistry of biological chemosensors, organic light‐emitting diodes, and inner‐shell electronic processes has been investigated by the SAC‐CI method. The electronic mechanism of the photo‐induced electron transfer has been clarified for the recently developed fluorescent probe. The absorption and emission spectra of the organic light‐emitting diodes such as polyphenylenevinylene and fluorene‐thiophene have been predicted in high accuracy. Various kinds of phenomena appearing in the core‐electronic processes such as shake‐up satellites, vibrational excitations, valence‐Rydberg coupling, and its thermal effect, have been accurately examined. The present works provides the useful basis for the theoretical investigations of the wide varieties of photochemistry.