New insight on hydrogen evolution reaction activity of the most exposure (0 1 1) surface and its monovacancy defect for FeP system: A theoretical perspective

•FeP has the metallic character, which is advantageous for HER catalytic activity.•The values of ΔGH* reveal that (0 1 1) surface has high HER catalytic activity.•(1 1 1) surface has optimal ΔGH* close-to-zero at 25% hydrogen coverages.•Monovacancy defect with Fe can significantly improve HER catalytic activity.