Equations of state of poly-$\alpha$-methylstyrene and polystyrene: First-principles calculations versus precision measurements

We show with a recently devised extended first-principles molecular dynamics method that calculated Hugoniots of poly-$\alpha$-methylstyrene agree well with precision experimental results of Kritcher et al. [Nature (London) 584, 51 (2020)] and Döppner et al. [Phys. Rev. Lett. 121, 025001 (2018)]. The deviation is smaller than 0.8%. This agreement does not sensitively rely on the approximations in the employed first-principles methods as long as underlying physics are well described, as illustrated in the calculation of equation of state for polystyrene covering the warm dense regime. These results may stimulate a broad range of quantitative investigations on warm dense matter that were not thought possible before, and may thus afford a new prospect to the field of inertial confinement fusion and high-energy-density physics.

Figure 1

EOS and Hugoniot comparisons for polystyrene, calculated using the ext-FPMD method [15] and the relay of the PIMC and the FPMD methods of Zhang et al. [26, 27], where (a) is typical EOS points calculated using the two methods; (b) is relative deviations of pressure between the two methods along isothermals; (c) is relative deviations of total energy between the two methods, and (d) is Hugoniots calculated from the two sets of EOS data. Note that in (b) and (c) the deviation between two adjacent horizontal lines is 2%, and only isothermals with the maximum deviation greater than 2% are displayed except the one of the highest temperature, i.e., $T=11145.31$ eV.

Figure 2

Calculated Hugoniot of poly-$\alpha$-methylstyrene compared with experimental measurements of Kritcher et al. [25], represented by red lines, and Döppner et al. [10], denoted by blue lines. Shadow areas display the experimental uncertainty in the measurements. (a) Stoichiometric influence of poly-$\alpha$-methylstyrene and polystyrene on the calculated Hugoniots. (b) Hugoniots with preheat effect compared with experimental results of Döppner et al. [10]. (c) Hugoniots with preheat effect compared with experimental results of Kritcher et al. [25]. (d) Influence of preheat-caused density variation on the Hugoniot.