• Matter and Radiation at Extremes
  • Vol. 5, Issue 6, 064403 (2020)
Dongdong Kang1, Kai Luo2, Keith Runge3, and S. B. Trickey4
Author Affiliations
  • 1Department of Physics, National University of Defense Technology, Changsha, Hunan 410073, People’s Republic of China
  • 2Earth and Planets Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015, USA
  • 3Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721, USA
  • 4Quantum Theory Project, Department of Physics and Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA
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    DOI: 10.1063/5.0025164 Cite this Article
    Dongdong Kang, Kai Luo, Keith Runge, S. B. Trickey. Two-temperature warm dense hydrogen as a test of quantum protons driven by orbital-free density functional theory electronic forces[J]. Matter and Radiation at Extremes, 2020, 5(6): 064403 Copy Citation Text show less

    Abstract

    We consider a steady-state (but transient) situation in which a warm dense aggregate is a two-temperature system with equilibrium electrons at temperature Te, ions at Ti, and TeTi. Such states are achievable by pump–probe experiments. For warm dense hydrogen in such a two-temperature situation, we investigate nuclear quantum effects (NQEs) on structure and thermodynamic properties, thereby delineating the limitations of ordinary ab initio molecular dynamics. We use path integral molecular dynamics (PIMD) simulations driven by orbital-free density functional theory (OFDFT) calculations with state-of-the-art noninteracting free-energy and exchange-correlation functionals for the explicit temperature dependence. We calibrate the OFDFT calculations against conventional (explicit orbitals) Kohn–Sham DFT. We find that when the ratio of the ionic thermal de Broglie wavelength to the mean interionic distance is larger than about 0.30, the ionic radial distribution function is meaningfully affected by the inclusion of NQEs. Moreover, NQEs induce a substantial increase in both the ionic and electronic pressures. This confirms the importance of NQEs for highly accurate equation-of-state data on highly driven hydrogen. For Te > 20 kK, increasing Te in the warm dense hydrogen has slight effects on the ionic radial distribution function and equation of state in the range of densities considered. In addition, we confirm that compared with thermostatted ring-polymer molecular dynamics, the primitive PIMD algorithm overestimates electronic pressures, a consequence of the overly localized ionic description from the primitive scheme.
    ZP=mP2πβ23NP/2s=1Pi=1Ndri(s)×expβs=1Pi=1N12mωP2(ri(s)ri(s+1))2+1PV({ri}(s)),(1)

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    Heff=s=1Pi=1Npi(s)22m+Veff,(2)

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    Veff=s=1Pi=1N12mωP2ri(s)ri(s+1)2+1Ps=1PV{ri}(s).(3)

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    mr̈i(s)=mωP22ri(s)ri(s+1)ri(s1)1PV{ri}(s)ri(s).(4)

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    ϵkin=32NPkBTis=1Pi=1N12mωP2ri(s)ri(s+1)2,(5)

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    ϵpot=1Ps=1PV{ri}(s),(6)

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    p=NPkBTiV13Vs=1Pi=1N[mωP2(ri(s)ri(s+1))2+1Pri(s)V({ri}(s))ri(s)],(7)

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    Ω[n]=F[n]+drv(r)μn(r),(8)

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    F[n]=Fs[n]+FH[n]+Fxc[n].(9)

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    FH[n]=12n(r,Te)n(r,Te)|rr|drdr.(10)

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    Fs[n]=Ts[n]TeSs[n],(11)

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    Fxc[n]=(T[n]Ts[n])Te(S[n]Ss[n])+(UeeFH[n]),(12)

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    δTs[n]δnTeδSs[n]δn+δFH[n]δn+δFxc[n]δn=μv(r).(13)

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    g(r)=ni(r)4πni,0r2ΔrPI,(14)

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    Rig=1Ps=1Pri(s)ric,(15)

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    Dongdong Kang, Kai Luo, Keith Runge, S. B. Trickey. Two-temperature warm dense hydrogen as a test of quantum protons driven by orbital-free density functional theory electronic forces[J]. Matter and Radiation at Extremes, 2020, 5(6): 064403
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