A Review of Studies on Strongly‐Coupled Coulomb Systems Since the Rise of DFT and SCCS‐1977

Abstract

The conferences on "Strongly Coupled Coulomb Systems" (SCCS) arose from the "Strongly Coupled Plasmas" meetings, inaugurated in 1977. The progress in SCCS theory is reviewed in an 'author-centered' frame to limit its scope. Our efforts, i.e., with François Perrot, sought to apply density functional theory (DFT) to SCCS calculations. DFT was then poised to become the major computational scheme for condensed matter physics. The ion-sphere models of Salpeter and others evolved into useful average-atom models for finite-T Coulomb systems, as in Lieberman's Inferno code. We replaced these by correlation-sphere models that exploit the description of matter via density functionals linked to pair-distributions. These methods provided practical computational means for studying strongly interacting electron-ion Coulomb systems like warm-dense matter (WDM). The staples of SCCS are wide-ranged, viz., equation of state, plasma spectroscopy, opacity (absorption, emission), scattering, level shifts, transport properties, e.g., electrical and heat conductivity, laser-and shock-created plasmas, their energy relaxation and transient properties etc. These calculations need pseudopotentials and exchange-correlation functionals applicable to finite-T Coulomb systems that may be used in ab initio codes, molecular dynamics, etc. The search for simpler computational schemes has proceeded via proposals for orbital-free DFT, statistical potentials, classical maps of quantum systems using classical schemes like HNC to include strong coupling effects (CHNC). Laughlin's classical plasma map for the fractional quantum Hall effect (FQHE) is a seminal example where we report new results for graphene.

Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime

“…The validity of this approach has been established in previous work, for the WDM systems investigated here and reviewed in Ref. [10]. The solution of the KS equation extends up to R c = 10r ws , defining a correlation sphere (CS) large enough for all electronic and ionic correlations with the central nucleus to have gone to zero.…”

“…The three conductivities σ ic , σ ib , and σ uf for Al, Li and C, are calculated via two first-principles methods where, however, both finally use a 'mean-free path' model to estimate the conductivity. The two methods are: (i) the neutral pseudoatom (NPA) method as formulated by Perrot and Dharma-wardana [6,[10][11][12] together with the Ziman formula, and (ii) the DFT+MD and KG approach as available in codes such as VASP and ABINIT [13], enabling us to assess the extent of the agreement among these theoretical methods and the available experiments. The liquid-metal experimental data are still the most accurate data on WDM systems available; they are used where possible to compare with calculations.…”

“…The NPA methods, e.g., that of Perrot and Dharmawardana, reduce the many-electron, many-ion problem to an effective one-electron, one-ion problem using DFT [10,11,48]. A Kohn-Sham (KS) calculation for a nucleus immersed in the plasma medium provides the bound and free KS states.…”

Finite-temperature quantum effects on confined charges

“…Here those self-consistent equations are replaced with the classical integral equations of HNC. This advantage has been stressed recently by Dharma-wardana [31,32].…”

“…Reviews of this latter work are given by Refs. [30][31][32]. The classical map method, although not broadly adopted, is a rare theoretical approach that can be applied broadly across the temperature-density plane and has demonstrated significant success to date.…”