Version Of Random Phase Approximation Research Articles

Zeptosecond Dynamics in Atoms: Fact or Fiction?

Photon exchange due to nuclear bremsstrahlung during nuclear collisions can cause Coulomb excitation in the projectile and the target nuclei. The corresponding process originated in nuclear timescales can also be observed in atomic phenomenon experimentally if it delayed by at least with an attosecond or longer timescales. We have found that this happens due to a mechanism involving the Eisenbud-Wigner-Smith time delay process. We have estimated photoionization time delays in atomic collisions utilizing the nonrelativistic version of random phase approximation with exchange and Hartree-Fock methods. We present three representative processes in which we can observe the phenomena in attosecond timescales even though they originate from excitations in the zeptosecond timescales. Thus the work represents an investigation of parallels between two neighboring areas of physics. Furthermore the present work suggests new possibilities for atomic physics research near the Coulomb barrier energy, where the laser is replaced by nuclear bremsstrahlung.

Exciton concentrations in thin films

Excitons in thin films are analyzed using Green's function method within the framework of Tyablikov's version of random phase approximation. The spectra of surface and bulk excitons were determined and the distribution of exciton concentrations over film layers was evaluated. It was shown that high surface concentrations could be achieved by decreasing of the dipole-dipole interaction of the molecules in surface layers.