Predicted Stabilities of High-Density P-N and H-N Extended Solids: A Combined Modeling and Experimental Study

Evolutionary structural search simulations were conducted to search for stable P-N and H-N network-type structures. Density functional theory-based calculations with SCAN functional of relevant high-pressure systems formed the basis for our approach. High-density covalently bonded structures were created in silico using variable and fixed concentration methods. Rank sorting of the most promising (viable) systems is initially based on thermodynamic stability assessments and direct comparison with our measured experimental X-ray diffraction (XRD) patterns. The high pressure stability of predicted systems was finally estimated from convex-hull plot at 0 K. Temperature effect on the stable structures were calculated using temperature dependent effective potential method (TDEP). XRD patterns were calculated using a virtual diffraction algorithm that computes kinematic diffraction intensities in three-dimensional reciprocal space. Direct computation of structure factors enables implementation of distinct atomic scattering factors for each atomic constituent. Evolution (or pressure dependence) of Raman spectra and elastic constants at high pressure were calculated and compared with experiment for the P-N extended solids.