Abstract

No abstract

The accuracy of local pseudopotentials (LPSs) is one of two major determinants of the fidelity of orbital-free density functional theory (OFDFT) simulations. We present a global optimization strategy for LPSs that enables OFDFT to reproduce solid and liquid properties obtained from Kohn-Sham DFT. Our optimization strategy can fit arbitrary properties from both solid and liquid phases, so the resulting globally optimized local pseudopotentials (goLPSs) can be used in solid and/or liquid-phase simulations depending on the fitting process. We show three test cases proving that we can (1) improve solid properties compared to our previous bulk-derived local pseudopotential generation scheme; (2) refine predicted liquid and solid properties by adding force matching data; and (3) generate a from-scratch, accurate goLPS from the local channel of a non-local pseudopotential. The proposed scheme therefore serves as a full and improved LPS construction protocol.

The appearance of a second excitation mode in the longitudinal and transverse collective dynamics of a series of liquid metals has been observed recently, either by inelastic X-ray scattering (IXS) or by first-principles molecular dynamics (FPMD). The phenomenon's origin is still uncertain, although some theories have been used with relative success to reproduce the FPMD results as a means to find an explanation for it (e.g., mode-coupling (MC) theory in liquid zinc [B. G. del Rio and L. E. González, Phys. Rev. B , 224201 (2017)]). For liquid tin (-Sn), the second excitation mode in the dynamic structure factor and longitudinal current spectrum was observed by IXS [S. Hosokawa , J. Phys.: Condens. Matter, 112101 (2013)]. By performing orbital-free density functional theory MD simulations of -Sn, we confirm the existence of a second excitation mode in the longitudinal and transverse collective dynamics and provide a theoretical explanation based on MC theory. Moreover, we introduce a new binary term in MC theory to better capture the negative minima present in the memory functions of the collective dynamics. These results confirm that the origin of the second excitation mode exhibited by the longitudinal and transverse collective dynamics in some liquid metals involves an indirect coupling of the longitudinal and transverse modes.