Complex Behavior of Fluid Lithium under Extreme Conditions

Kietzmann, André; Redmer, R.; Desjarlais, M. P.; Mattsson, Thomas R.

doi:10.1103/physrevlett.101.070401

Cited by 58 publications

(55 citation statements)

References 31 publications

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“…Hence the use of this functional in WDM studies may lead to uncontrolled or unknown errors. Furthermore, previous studies, e.g., Pozzo et al [7], Kietzmann et al [39], show that the PBE functional successfully predicts conductivities. Those conductivities, if recalculated with the HSE functional are most likely to be in serious disagreement with the experimental data.…”

Section: Xc-functionals and The Al Conductivitymentioning

confidence: 99%

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

et al. 2017

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We study the conductivities σ of (i) the equilibrium isochoric state (σis), (ii) the equilibrium isobaric state (σ ib ), and also the (iii) non-equilibrium ultrafast matter (UFM) state (σ uf ) with the ion temperature Ti less than the the electron temperature Te. Aluminum, lithium and carbon are considered, being increasingly complex warm dense matter (WDM) systems, with carbon having transient covalent bonds. First-principles calculations, i.e., neutral-pseudoatom (NPA) calculations and density-functional theory (DFT) with molecular-dynamics (MD) simulations, are compared where possible with experimental data to characterize σic, σ ib and σ uf . The NPA σ ib are closest to the available experimental data when compared to results from DFT+MD, where simulations of about 64-125 atoms are typically used. The published conductivities for Li are reviewed and the value at a temperature of 4.5 eV is examined using supporting X-ray Thomson scattering calculations. A physical picture of the variations of σ with temperature and density applicable to these materials is given. The insensitivity of σ to Te below 10 eV for carbon, compared to Al and Li, is clarified.

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Section: Xc-functionals and The Al Conductivitymentioning

confidence: 99%

“…In Fig. 6 we have attempted to compare the Oak Ridge experimental data for liquid lithium with the DFT+MD+KG calculations of Kietzmann et al [39]. We use their calculations as a function of density for 600K and 1500K.…”

Section: The Conductivities Of Wdm Lithiummentioning

confidence: 99%

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

et al. 2017

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“…But as electronic structure methods are applied in ever more esoteric areas, the need to account for the finite temperature of electrons increases. Phenomena where such effects play a role include rapid heating of solids via strong laser fields [2], dynamo effects in giant planets [3], magnetic [4,5] and superconducting phase transitions [6,7], shock waves [8,9], warm dense matter [10], and hot plasmas [11][12][13].…”

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confidence: 99%

Exact Conditions in Finite-Temperature Density-Functional Theory

et al. 2011

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Density functional theory (DFT) for electrons at finite temperature is increasingly important in condensed matter and chemistry. Exact conditions that have proven crucial in constraining and constructing accurate approximations for ground-state DFT are generalized to finite temperature, including the adiabatic connection formula. We discuss consequences for functional construction.Because of the small mass ratio between electrons and nuclei, standard electronic structure calculations treat the former as being in their ground state, but routinely account for the finite temperature of the latter, as in ab initio molecular dynamics [1]. But as electronic structure methods are applied in ever more esoteric areas, the need to account for the finite temperature of electrons increases. Phenomena where such effects play a role include rapid heating of solids via strong laser fields [2], dynamo effects in giant planets [3], magnetic [4,5] and superconducting phase transitions [6,7], shock waves [8,9], warm dense matter [10], and hot plasmas [11][12][13].Within density functional theory, the natural framework for treating such effects was created by Mermin [14]. Application of that work to the Kohn-Sham (KS) scheme at finite temperature also yields a natural approximation: treat KS electrons at finite temperature but use groundstate exchange-correlation (XC) functionals. This works well in recent calculations [8,10], where inclusion of such effects is crucial for accurate prediction. This assumes that finite-temperature effects on exchange-correlation are negligible relative to the KS contributions, which may not always be true.The uniform electron gas at finite temperature (also called the one-component plasma) has been well-studied, and has in the past provided the natural starting point for DFT studies of such finite-temperature XC effects, as input into the local density approximation (LDA) at finite T [15]. However, the LDA is too inaccurate for most modern applications of DFT, and almost all recent calculations use a generalized gradient approximation or hybrid with exchange [16]. The errors of LDA would typically be enormous relative to the temperature corrections we seek, especially for correlation, and so could lead to quite misleading results. Accurate calculation of finite temperature contributions requires accurate approximate functionals. Magnetic phase transitions bear an additional difficulty: The low-lying excitations are collective, i.e., magnons whose description requires non-collinear version of spin-DFT. Hence, a finite-temperature version of spin-DFT involving only spin-up and spin-down densities and thus only spin-flip excitations, is bound to fail in predicting, e.g., the critical temperature [4].The most fundamental steps toward both understanding a functional and creating accurate approximations are deriving its inequalities from the variational definition of the functional. These yield both the signs of energy contributions and, via uniform scaling of the spatial coordinates, basic equalities and...

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“…(11,25). However no attempts have been made to understand what happens at high pressures and temperatures.…”

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confidence: 99%

High-temperature high-pressure phases of lithium from electron force field (eFF) quantum electron dynamics simulations

Goddard

2011

Proc. Natl. Acad. Sci. U.S.A.

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We recently developed the electron force field (eFF) method for practical nonadiabatic electron dynamics simulations of materials under extreme conditions and showed that it gave an excellent description of the shock thermodynamics of hydrogen from molecules to atoms to plasma, as well as the electron dynamics of the Auger decay in diamondoids following core electron ionization. Here we apply eFF to the shock thermodynamics of lithium metal, where we find two distinct consecutive phase changes that manifest themselves as a kink in the shock Hugoniot, previously observed experimentally, but not explained. Analyzing the atomic distribution functions, we establish that the first phase transition corresponds to (i) an fcc-to-cI16 phase transition that was observed previously in diamond anvil cell experiments at low temperature and (ii) a second phase transition that corresponds to the formation of a new amorphous phase (amor) of lithium that is distinct from normal molten lithium. The amorphous phase has enhanced valence electron-nucleus interactions due to localization of electrons into interstitial locations, along with a random connectivity distribution function. This indicates that eFF can characterize and compute the relative stability of states of matter under extreme conditions (e.g., warm dense matter).wavepacket dynamics | interstitial electron model | symmetry breaking T here are great uncertainties in the properties of matter at the high compression (several times ambient densities) and high temperatures (20,000-2,000,000 K) characteristic of deep interiors of giant planets (1), conditions of thermonuclear fusion, and phenomena generated by shocks from planetary impact (2). New methods for experimental study of these regimes are being developed (National Ignition Facility at Lawrence Livermore National Laboratory, Z-Pinch at Sandia National Laboratory) that generate data about materials under extreme conditions. However, theoretical and computational methods used to predict properties of warm dense matter [high temperatures (T), high pressures (P), and under rapidly changing conditions] have serious shortcomings leading to considerable uncertainties due to high degrees of electronic excitation, structural and electronic heterogeneity, and complex transient dynamics. This contrasts with the situation at room temperature (RT), where a wealth of structural and energetic data on compressed phases is available via experiments in diamond anvil cells and gas guns (3-5), and from theoretical studies such as density functional theory (DFT).To provide fresh insight into the dynamical properties of warm dense matter, we developed the eFF (electron force field) methodology that explicitly solves the time-dependent Schrödinger equation including all two-body interactions, with the restrictions that the electrons are described as Gaussian wave packets and that the wavefunction is described as a Hartree product (with exchange terms replaced by a spin dependent Hamiltonian). The eFF makes it practical to describe the non...

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Complex Behavior of Fluid Lithium under Extreme Conditions

Cited by 58 publications

References 31 publications

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

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

Exact Conditions in Finite-Temperature Density-Functional Theory

High-temperature high-pressure phases of lithium from electron force field (eFF) quantum electron dynamics simulations

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