Large Atomic Systems Research Articles

Non-adiabatic quantum molecular dynamics: basic formalism and case study

A general formalism is presented that treats selfconsistently and simultaneously classical atomic motion and quantum electronic excitations in dynamical processes of atomic many-body systems (non-adiabatic quantum molecular dynamics). On the basis of time-dependent density functional theory, coupled highly non-linear equations of motion are derived for arbitrary basis sets for the time-dependent Kohn-Sham orbitals. Possible approximations to make the approach practical for large atomic cluster systems are discussed. As a first application of the still exact equations of motion, non-adiabatic effects in the scattering of H++H, as a case study, are investigated.

Molecular dynamics for proteins: Performance evaluation on massively parallel computers based on mesh networks using a space decomposition approach

Parallel computing seems to be the solution for molecular dynamics of large atomic systems, such as proteins in water environments, but the simulation time critically depends on the processor allocation strategy. A study of the optimal processor allocation based on a space decomposition algorithm for single instruction multiple data flow mesh computers is presented. A particular effort has been made to identify the best criterion according to which the atoms can be allocated to the processors using a spatial decomposition approach. The computing time depends on the granularity of the space decomposition among processing elements and on the ratio between the computation power of processing elements and the communication speed of the interprocessor network. © 1996 by John Wiley & Sons, Inc.

Some comments on the use of phased angular momentum states in the theory of coherent spontaneous emission from large systems

We stress the importance of using phased atomic states when describing coherent spontaneous emission from large atomic systems. A sufficient criterion for the existence of a preferred direction of emission is deduced from dynamical arguments.

Relativistic and Correlation Effects for Optical Levels of Large Atomic Systems: Application to Tl ii

The effects of relativity and correlation on bound levels of large atomic systems are investigated by using the low-Z Pauli approximation for the Hamiltonian. A linear combination of Slater determinants is used to approximate the wavefunctions. The radials are obtained from the Hartree–Fock–Slater equation with six potential forms, and the coefficients are found by application of the variational principle. Results are obtained for a matrix element involving any two configurations composed of a closed core and two valence spin–orbitals. Application is then made to some of the bound levels of Tl ii. The average error in the energy levels (the ground state is the reference level) is found to be 5% as compared to the average error of 25% in the nonrelativistic results of Beck. Both correlation and relativistic effects are important.

High density and large atomic number systems for gas bubble chambers

The experimental difficulties in the use of highdensity, high- temperature, corrosive liquids in bubble chambers are discussed. It is pointed out that many of the difficulties might be removed by giving up superheated liquids and making use of different principles such as supersaturated gas-liquid solutions which can be radiation sensitive at room temperature or temperatures not far above room temperature. A bubble chamber using the above principles is described. Experimental results are tabulated. (A.C.)