Evolutionary Search for Superconducting Phases in the Lanthanum-Nitrogen-Hydrogen System with Universal Neural Network Potential PFP

We explored thermodynamically stable and superconducting phases in the lanthanum-nitrogen-hydrogen system (La $$_{x}$$ x N $$_{y}$$ y H $$_{1-x-y}$$ 1 - x - y , $$0 \le x \le 1$$ 0 ≤ x ≤ 1 , $$0 \le y \le 1$$ 0 ≤ y ≤ 1 ) at pressure of 20 GP using an evolutionary construction scheme of a formation-energy convex hull based on density functional theory calculations. To accelerate the exploration, we optimized only the structures selected as stable and moderately metastable compounds by universal neural network potential (PFP) calculations. Following the constructed convex hull diagram, we investigated the superconductivity for the predicted compounds and found that metastable La $$_2$$ 2 NH $$_2$$ 2 and La $$_2$$ 2 N $$_5$$ 5 H $$_2$$ 2 show the $$T_\textrm{c}$$ T c values of 14.41 K and 12.08 K, respectively.