Density-functional theory (DFT) has been widely used for important applications to better understand the physics and chemistry of nature from near-ambient to extreme conditions. Thorough understanding of the properties of warm-dense matter, nonideal, and "exotic" plasmas holds the key to unravel many mysteries in high-energy-density physics, planetary, and astrophysical sciences. Reliably predicting the transport and optical properties of matter at such extreme conditions heavily depends on the accuracy of exchange-correlation (XC) density functionals required by the DFT method.

The results of this project have made an important contribution to the formal development of density-functional theory by developing two new classes of thermal XC functionals. Theoretical grounds of thermal hybrid exchange-correlation have been provided. A new thermal hybrid XC based on a mixture of the thermal Karasiev-Dufty-Trickey (KDT16) DFT XC with the thermal Hartree-Fock exact exchange, referred as KDT0, has been introduced. Application of the new KDT0 thermal hybrid to static calculations of electronic band gap and band structure of several materials at a wide range of temperatures show that KDT0 provides a significant improvement to the ground-state (nonthermal) approximations including ground-state hybrids. Next, strategies for thermalization of the ground-state meta-generalized gradient approximation (meta-GGA) XC functionals have been provided. A simple but accurate scheme was implemented, leading to the thermal strongly constrained and appropriately normed Laplacian dependent (T-SCAN-L) meta-GGA exchange-correlation. Employing the new T-SCAN-L functional, an unprecedented accuracy for helium equation of state (≤1%), as demonstrated by the comparison to path integral Monte Carlo simulations, has been achieved. Newly developed thermal hybrid and thermal meta-GGA functionals open new perspectives for improving the accuracy of DFT-based applications in warm dense matter and plasma regimes, increasing the predictive power of DFT calculations with the capability to generate theoretical data that are thermodynamically consistent across temperature regimes.

Applications of density functionals and methodologies developed in this project provided a better understanding the physics of extreme matter at the atomic level and contributed to the resolution of a few longstanding problems: (1) Characterization of the molecular-to-atomic liquid-liquid phase transition in dense hydrogen is a problem of longstanding and controversy. Large-scale molecular dynamics simulations provided the numerical evidence for subcritical behavior of high-pressure liquid hydrogen. (2) X-ray spectral measurements for superdense Cu-doped CH plasma have been reported. Developed fully consistent theoretical treatment based on density-functional theory demonstrated a good agreement with experimental measurements. (3) Developed all-electron pseudopotential datasets were used to study superdense Fe-Zn plasma mixtures at an elevated temperature. DFT-based calculations predicted two new atomic-physics phenomena, interspecies radiative transition (IRT) and the breaking down of the dipole-selection rule for radiative transitions between deep K- and L-shell electrons. (4) Application of the new thermal hybrid KDT0 and thermal meta-GGA T-SCAN-L exchange-correlation functionals to treat CH-based materials, used as an ablator material in inertial confinement fusion targets, at warm dense thermodynamic conditions demonstrated that the thermal and inhomogeneity XC effects are crucial for accurate predictions and interpretation of experimental data. The simulated optical reflectivity of shocked CH as an indicator of the insulator-metal transition is in perfect accord with experimental data.

During the course of this project, three graduate students were involved in research, mentored and trained. Once the graduate students learned the fundamentals of density functional theory and became knowledgeable and experienced users of DFT computational packages, they made important contributions in the research agenda by completing assigned tasks. Three papers (published or under review) were first-authored by graduate students. Two other papers listed graduate students as co-authors. A post-doc who worked on this project became an expert in theoretical methods of high-energy-density physics and software development. Eventually the post-doc was hired as a Research Engineer at the University of Rochester's Laboratory for Laser Energetics.

Another outcome of the project includes the development of all-electron pseudopotential datasets transferable to the extreme conditions of high temperature and high pressure and software development. All-electron pseudopotential data sets have been developed for several low-Z and mid-Z elements. New thermal functionals developed in the project have been implemented in large-scale simulation packages widely used by national labs and in the scientific community in general. Developed all-electron pseudopotential datasets and enhanced software are currently available to the community in the form of patches to standard distribution versions upon request.

Last Modified: 09/15/2022
Modified by: Valentin V Karasev