اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدFirst-Principles Calculation of Principal Hugoniot and K-Shell X-ray Absorption Spectra for Warm Dense KCl
238
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Principal Hugoniot and K-shell X-ray absorption spectra of warm dense KCl are calculated using the first-principles molecular dynamics method. Evolution of electronic structures as well as the influence of the approximate description of ionization on pressure (caused by the underestimation of the energy gap between conduction bands and valence bands) in the first-principles method are illustrated by the calculation. Pressure ionization and thermal smearing are shown as the major factors to prevent the deviation of pressure from global accumulation along the Hugoniot. In addition, cancellation between electronic kinetic pressure and virial pressure further reduces the deviation. The calculation of X-ray absorption spectra shows that the band gap of KCl persists after the pressure ionization of the $3p$ electrons of Cl and K taking place at lower energy, which provides a detailed understanding to the evolution of electronic structures of warm dense matter.
قيم البحث
اقرأ أيضاً
A precise calculation that translates shifts of X-ray K-absorption edges to variations of thermodynamic properties allows quantitative characterization of interior thermodynamic properties of warm dense plasmas by X-ray absorption techniques, which p
rovides essential information for inertial confinement fusion and other astrophysical applications. We show that this interpretation can be achieved through an improved first-principles method. Our calculation shows that the shift of K-edges exhibits selective sensitivity to thermal parameters and thus would be a suitable temperature index to warm dense plasmas. We also show with a simple model that the shift of K-edges can be used to detect inhomogeneity inside warm dense plasmas when combined with other experimental tools.
Exploring and understanding ultrafast processes at the atomic level is a scientific challenge. Femtosecond X-ray Absorption Spectroscopy (XAS) is an essential experimental probing technic, as it can simultaneously reveal both electronic and atomic st
ructures, and thus unravel their non-equilibrium dynamic interplay which is at the origin of most of the ultrafast mechanisms. However, despite considerable efforts, there is still no femtosecond X-ray source suitable for routine experiments. Here we show that betatron radiation from relativistic laser-plasma interaction combines ideal features for femtosecond XAS. It has been used to investigate the non-equilibrium transition of a copper sample brought at extreme conditions of temperature and pressure by a femtosecond laser pulse. We measured a rise time of the electron temperature below 100 fs. This first experiment demonstrates the great potential of the betatron source and paves the way to a new class of ultrafast experiments.
An efficient first principles approach to calculate X-ray magnetic circular dichroism (XMCD) and X-ray natural circular dichroism (XNCD) is developed and applied in the near edge region at the K-and L1-edges in solids. Computation of circular dichroi
sm requires precise calculations of X-ray absorption spectra (XAS) for circularly polarized light. For the derivation of the XAS cross section, we used a relativistic description of the photon-electron interaction that results in an additional term in the cross-section that couples the electric dipole operator with an operator $mathbf{sigma}cdot (mathbf{epsilon} times mathbf{r})$ that we name spin-position. The numerical method relies on pseudopotentials, on the gauge including projected augmented wave method and on a collinear spin relativistic description of the electronic structure. We apply the method to the calculations of K-edge XMCD spectra of ferromagnetic iron, cobalt and nickel and of I L1-edge XNCD spectra of $alpha$-LiIO3, a compound with broken inversion symmetry. For XMCD spectra we find that, even if the electric dipole term is the dominant one, the electric quadrupole term is not negligible (8% in amplitude in the case of iron). The term coupling the electric dipole operator with the spin-position operator is significant (28% in amplitude in the case of iron). We obtain a sum-rule relating this new term to the spin magnetic moment of the p-states. In $alpha$-LiIO3 we recover the expected angular dependence of the XNCD spectra.
The structure of the fluid carbon phase in the pressure region of the graphite, diamond, and BC8 solid phase is investigated. We find increasing coordination numbers with an increase in density. From zero to $30$ GPa, the liquid shows a decrease of p
acking efficiency with increasing temperature. However, for higher pressures, the coordination number increases with increasing temperature. Up to $1.5$ eV and independent of the pressure up to $1000$ GPa, a double-peak structure in the ion structure factors exists, indicating persisting covalent bonds. Over the whole pressure range from zero to $1000$ GPa, the fluid structure and properties are strongly determined by such covalent bonds.
A scheme for analyzing Thomson scattering of x-rays by warm dense matter, based on the average-atom model, is developed. Emphasis is given to x-ray scattering by bound electrons. Contributions to the scattered x-ray spectrum from elastic scattering b
y electrons moving with the ions and from inelastic scattering by free and bound electrons are evaluated using parameters (chemical potential, average ionic charge, free electron density, bound and continuum wave functions, and occupation numbers) taken from the average-atom model. The resulting scheme provides a relatively simple diagnostic for use in connection with x-ray scattering measurements. Applications are given to dense hydrogen, beryllium, aluminum, titanium, and tin plasmas. At high momentum transfer, contributions from inelastic scattering by bound electrons are dominant features of the scattered x-ray spectrum for aluminum, titanium, and tin.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
