The nitrogen dimer as both a fundamental building unit in designing a new type of nitrides,and a material gene associated with high electrical and thermal conductivities is investigated by first principles calculations.The results indicate that the predicted SiN4 is structurally stable and reasonably energy-favored with a striking feature in its band structure that exhibits free electron-like energy dispersions.It possesses a high electrical conductivity (5.07 × 105 S/cm) and a high thermal conductivity (371 W/m·K) comparable to copper.The validity is tested by isostructural AlN4 and SiC4.It is demonstrated that the nitrogen dimers can supply a high density of delocalized electrons in this new type of nitrides.