A first-principles study of physical properties of monatomic structures of B, C, N, and O

We have performed a series of studies on the properties of monatomic solid boron (B), carbon (C), nitrogen (N) and oxygen (O) under high pressure with a first-principles method. Four structures with different coordination numbers, i.e., cubic diamond, simple cubic, body center cubic and face center cubic structures, are calculated to investigate the relationship of physical properties and coordination numbers. Our investigation shows that all the four elements under high pressure favor a higher coordination number structure and become more metallic like. The bulk moduli have also been investigated, showing that atomic volume is the most important factor that determines the bulk moduli. The effects of composition and coordination on bulk moduli are secondary for B, C, N, and O. The investigation also reveals that the species having a small atomic volume will have a large bulk modulus. As expected, the bulk modulus of diamond is the largest one we studied. We found that the bulk modulus of carbon in simple cubic structure (3.37 Mbar) is slightly less than that of c-BN (3.67 Mbar), the second hardest material in the world. The bulk moduli of B in fee structure (2.8 Mbar) and N in simple cubic structure (2.57 Mbar) are larger than that of SiC (2.24 Mbar).