Spin-orbit interaction in molecular photoelectron spectra An intermediate coupling approach

A new and general semiempirical method for calculating ionization energies of molecules containing heavy atoms is presented. The extended Hückel hamiltonian is amended with a phenomenological one-electron spin-orbit interaction operator, and ionization energies are equated to orbital energies according to Koopmans' theorem. Calculations are presented for molecules with Br and I as heavy atoms. The systems considered are the hydrogen halides, diatomic halogens and interhalogens, haloacetylenes, halomethanes, and boron trihalides. Good agreement with the observed spin-orbit splitting is obtained. New assignments are proposed for the trihalides considered.     

Symplectic-energy-first integrators of discrete mechanico-electrical dynamical systems

A discrete total variation calculus with variable time steps is presented for mechanico-electrical systems where there exist non-potential and dissipative forces. By using this discrete variation calculus, the symplectic-energy-first integrators for mechanico-electrical systems are derived. To do this, the time step adaptation is employed. The discrete variational principle and the Euler--Lagrange equation are derived for the systems. By using this discrete algorithm it is shown that mechanico-electrical systems are not symplectic and their energies are not conserved unless they are Lagrange mechanico-electrical systems. A practical example is presented to illustrate these results.     

Isospin effects of projectile fragmentation in a Boltzmann-Langevin approach

The iso spin effects of projectile fragmentation at intermediate energies are investigated using an iso spindependent Boltzmann-Langevin model.The collisions of mass-symmetric reactions including ~(58)Fe,~(58)Ni+~(58)Fe,and~(58)Ni at intermediate energies,in the 30 to 100 MeV/A range,are studied for different symmetry energies.Yield ratios of the isotopic,isobaric,and isotonic pairs of fragments from the intermediate-mass region using three symmetry energies are extracted as functions of the N/Z ratio of the composite systems in the entrance channel and the incident energies.It is found that the yield ratios are sensitive to symmetry energies,especially for neutron-rich systems,and the calculations using soft symmetry energy are closer to the experimental data.The iso spin effect is stronger for the soft symmetry energy,owing to the competition of the repulsive Coulomb force and the symmetry energy attractive force on the proton.For the first time,the splits are presented,revealing a transition from the iso spin equilibrium at lower energies to translucency at intermediate energies.The results show a degree of transparency in that intermediate mass fragments undergo a transition from dependence on the composite systems in the entrance channel to reliance on the projectile and target nuclei.     

Molecular physics and chemistry applications of quantum Monte Carlo

We discuss recent work with the diffusion quantum Monte Carlo (QMC) method in its application to molecular systems. The formal correspondence of the imaginary-time Schrödinger equation to a diffusion equation allows one to calculate quantum mechanical expectation values as Monte Carlo averages over an ensemble of random walks. We report work on atomic and molecular total energies, as well as properties including electron affinities, binding energies, reaction barriers, and moments of the electronic charge distribution. A brief discussion is given on how standard QMC must be modified for calculating properties. Calculated energies and properties are presented for a number of molecular systems, including He, F, F^?, H₂, N, and N₂. Recent progress in extending the basic QMC approach to the calculation of “analytic” (as opposed to finite-difference) derivatives of the energy is presented, together with an H₂ potential-energy curve obtained using analytic derivatives.     

Excitons and electron-hole plasma in quasi-two-dimensional systems

A theoretical study of many-body effects in quasi-two-dimensional electron-hole systems is presented. The renormalized single-particle energies and the exciton binding energy are calculated as functions of the carrier density and temperature. A simple model for the nonlinear excitonic absorption and refraction is proposed.     

Statistical theory of hot nuclei and high spin states

The hot rotating compound systems formed in heavy ion collisions are studied using the statistical theory with a view to determine the spin and temperature dependence of nuclear shapes. Shape transitions are observed for these systems at particular spin values. The neutron and proton separation energies for heavier high spin systems have been evaluated. Results are presented for ₇₀ ¹⁷⁰ Yb and ₇₈ ¹⁹⁴ Pt.     

Free energies of ionic nanoclusters. Solid and coexistent solid-liquid states

A strategy to overcome some specific problems associated to the computation of free energies in clusters is presented. Free energies and entropies of solid KCl nanoclusters are determined by thermodynamic integration, and Watanabe and Reinhardt’s dynamical method, based on molecular dynamics simulations. The values are in good agreement with experimental data. From a previous theoretical prediction of the caloric curve, T(E), for the coexistence region, an equation is derived to compute the free energies of the clusters at the solid-liquid coexistence. The results are discussed in the context of the thermodynamic stability of phase coexistent states for finite and infinite systems, yielding consistent conclusions.     

Second-order picture of correlation effects in closed-shell atoms

Results of many calculations of the MP2 correlation energies for ground states of closed-shell atoms (referred to as MP2/CA energies) are presented and studied. Special attention is paid to laying down rules which govern the dependence on the nuclear charge (Z dependence) and on the number of electrons (N dependence) of (a) the partial wave (PW) increments to the second-order pair energies, (b) the second-order pair energies, and (c) the configurational pair energies. It has been found that these energy increments disclose many regularities useful from both the physical and computational points of view. Some of the MP2/CA increments are quasi-transferable between similar systems. The results obtained are used as a starting point for an extensive discussion of the methodological significance of MP2/CA studies, and for indicating various actual and potential areas of application of the MP2/CA approach in many-electron theory.     

Accurate vibrational energy spectra and dissociation energies of some diatomic electronic states

An algebraic method (AM) used to study the full vibrational spectra of diatomic systems, and an analytical formula used to calculate accurate molecular dissociation energies are applied to study the full vibrational spectra and molecular dissociation energies of some electronic states of homonuclear and heteronuclear diatomic molecules and diatomic ions. Studies show that the AM method and the analytical expression are reliable and economical physical methods for studying full vibrational spectra and molecular dissociation energies of diatomic electronic systems theoretically. They are particularly useful for those diatomic systems whose highlying vibrational energies may not be available.     

Accurate vibrational energy spectra and dissociation energies of some diatomic electronic states

An algebraic method (AM) used to study the full vibrational spectra of diatomic systems, and an analytical formula used to calculate accurate molecular dissociation energies are applied to study the full vibrational spectra and molecular dissociation energies of some electronic states of homonuclear and heteronuclear diatomic molecules and diatomic ions. Studies show that the AM method and the analytical expression are reliable and economical physical methods for studying full vibrational spectra and molecular dissociation energies of diatomic electronic systems theoretically. They are particularly useful for those diatomic systems whose high-lying vibrational energies may not be available.      

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.     

Effects of QED and Beyond from the Atomic Binding Energy

Atomic binding energies are calculated at utmost precision. A report on the current status of Lamb-shift predictions for hydrogenlike ions, including all quantum electrodynamical corrections to first and second order in the fine structure constant α is presented. All relevant nuclear effects are taken into account. High-precision calculations for the Lamb shift in hydrogen are presented. The hyperfine structure splitting and the g factor of a bound electron in the strong electromagnetic field of a heavy nucleus is considered. Special emphasis is also put on parity violation effects in atomic systems. For all systems possible investigations beyond precision tests of quantum electrodynamics are considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

E.P.R. evidence for the structuring effect of alcohol in water

A computational scheme for frequency-dependent polarizabilities of open-shell systems by coupled Hartree-Fock perturbation theory is presented. It allows the simultaneous approximate prediction of the involved electronic transition energies and can trivially be extended to imaginary values of the frequency. As a simple application, the dipole polarizability and some related properties of Li atoms are evaluated, the agreement with previous estimates being excellent.     

理论离实验有多远?——用代数方法精确研究双原子分子的完全振动能谱和离解能

本文较系统地简介了双原子分子振动能谱和离解能的研究历史、现状及若干研究方法,重点介绍了孙卫国等最近建立的研究双原子分子完全振动能谱的代数方法(AM)和计算双原子分子离解能的新物理公式。然后应用AM方法和离解能新公式对一批同核和异核双原子分子,以及双原子分子离子电子态的完全振动能谱和离解能进行了研究。结果表明,AM方法和新建立的离解能解析式相结合的理论方法对研究双原子分子及离子的完全振动能谱和离解能是行之有效的、简单经济的物理方法,为实验技术难以精确测量其高激发振动能级或离解能的双原子分子或离子体系提供了获得精确的完全振动能谱和体系离解能的一种理论新方法。     

Recent Experiments Involving Few-Nucleon Systems

Recent experimental results are presented for reactions involving A = 3 to A = 6 nuclear systems. The emphasis is on unique data obtained at new experimental facilities. It is shown that the inertial confinement fusion facilities OMEGA and NIF provide a largely unexpected opportunity for experimental few-body physics to both obtain data of unprecedented quality and extend previous measurements to energies not accessible in the past. Whenever possible, data are compared to state-of-the-art theoretical calculations.     

Multicentred QM/QM methods for overlapping model systems

An improved, more general method for performing multicentred integrated QM/QM calculations is presented. The new approach allows the multicentred approximation to be extended to overlapping model systems, removing a significant limitation of the original approach. The usefulness and numerical accuracy of the equations presented are confirmed via some applications to dipole–dipole, charge–dipole and charge–charge complexes. The method performs well for all of these complexes, which range from very weakly to very strongly bound and in which non-additivity effects on interaction energies range from 0.2 to 17kcalmol^?1.     

On nuclear states of [`(K)] \bar K mesons

The search for nuclear states of $ \bar K $ \bar K mesons poses interesting problems for the nuclear and low energy hadron physics: the behavior of tightly bound nuclear systems with strongly correlated impurities, the new kind of binding mechanisms and the extension of effective low energy theories to the strange sector. These problems are briefly presented and a method of variational calculation of the binding energies is discussed.     

Midrapidity production of secondaries in pp collisions at RHIC and LHC energies in the quark–gluon string model

We consider the phenomenological implications of the assumption that baryons are systems of three quarks connected through a gluon string junction. The transfer of baryon number in rapidity space due to the string junction propagation is considered in detail. At high energies this process leads to a significant effect on the net baryon production in hN collisions at midrapidities. The numerical results for midrapidity inclusive densities of different secondaries in the framework of the quark–gluon string model are in reasonable agreement with the experimental data. One universal value, λ≃0.25, for the strangeness suppression parameter correctly describes the yield ratios of Λ/p, Ξ/Λ, and Ω/Ξ. The predictions for pp collisions at LHC energies are also presented. PACS 25.75.Dw