Numerical Studies On Electron And Ion Dynamics In Strong Fields And Dense Plasmas

Lasers serve as the foundation of modern strong-field physics and have become indispensable tools for investigating physical processes in different areas ranging from atomic to particle physics.The recent laser technologies are capable of tracking electronic and structural dynamics on the atto-to few femtosecond time scales,triggering or influencing some fundamental processes of quantum electrodynamics,and also depositing in a short time massive amounts of energy on a solid to create dense plasma.The goals of studies in strong-field physics are to understand and control these processes.The properties of dense plasmas are crucial for astrophysical simulations and realizations of inertial confinement fusion(ICF).We develop a parallel Cartesian-grid-based time-dependent Schr?dinger equation solver(PCTDSE)for modeling laser–atom interactions.It can calculate the single-electron dynamics in arbitrary time-dependent vector potentials.We use a split-operator method combined with fast Fourier transforms(FFT),on a three-dimensional(3D)Cartesian grid.Parallelization is realized using a 2D decomposition strategy based on the Message Passing Interface(MPI),which results in a good parallel scaling on current supercomputers.We give sample applications for the hydrogen atom using the benchmark problems coming from the references and obtain consistent results.The extensions to other applications are straightforward with minimal modifications of the source code.On the basis of PCTDSE,we develop a parallel time-dependent Dirac eqution solver which is applicable to the relativistically quantum-mechanical simulations of spin-1/2particles in arbitrary time-and spatial-dependent electromagnetic fields.The program supports self-adaptive grid,making full use of the possible spatial locality of the wave function,which is important for practical use.We have verified the correctness of the program within a large range of applications.The role of spin in laser-matter interactions has aroused wide concerns due to emerging high intensity laser facilities.Especially,there is a revival of the old problem of how a relativistic particle with spin moves through an inhomogeneous external field.We calculate the electron spin-dependent dynamics in linearly polarized plane-wave and standing-wave field by solving three-dimensional Dirac equation and classical equations of motion taking into account the spin degree of freedom.True three-dimensional motions moving out of the polarization-propagation plane are identified.In a plane-wave field,the center-of-mass of quantum wave packet is consistent with the trajectory of classical particle.However,in a standing-wave field,the wave packet splits into different parts,we use an ensemble of classical particles to mimic the quantum behavior.We develop a multi-ion molecular dynamics(MIMD)method and apply it to calculate the self-diffusion coefficients of ions with different charge-state in the warm dense matter(WDM)regime.First,self-consistent calculations of electron structures of different charge-state ions in the ion spheres are carried out,with the ion-sphere radii being determined by the plasma density and the ion charges.The ionic fraction is then obtained by solving the Saha equation,taking account of interactions among different charge-state ions in the system,and ion-ion pair potentials are computed using the modified GordonKim method in the framework of the temperature-dependent density functional theory on the basis of the electron structures.Finally,MIMD is used to calculate ionic self-diffusion coefficients from the velocity correlation function according to the Green-Kubo relation.A comparison with the results of the average-atom model shows that different statistical processes will influence the ionic diffusion coefficient in the WDM regime.