Although topologically nontrivial properties are normally associated with insulating phases, recent developments have shown that (semi)metallic phases can also be topological. In this talk, I will survey recent developments regarding the topological classifications of (semi)metallic materials in terms of crystal symmetries [1,2]. As a concrete examples, I will present results about the recently discovered compound Ca3P2 , which has a line of Dirac nodes near the Fermi energy. I will discuss the topological properties of Ca3P2 in terms of a low-energy effective theory and a tight-binding model, derived from ab initio DFT calculations. The microscopic model for Ca3P2 shows that the drumhead surface states have a rather weak dispersion, which implies that correlation effects are enhanced at the surface of Ca3P2. Furthermore, I will discuss the parity anomaly that exists in this nodal-line semimetal and show how it is connected to unusual transport phenomena. If time permits, I will also survey the topological properties of the Dirac materials A3EO , where A denotes an alkaline earth metal, while E stands for Pb or Sn. I will discuss the magnetic properties of this Dirac system and show that a strong Zeeman field splits the gapped Dirac cones into ungapped Weyl points, which are protected by a quantized Chern number.
 Ching-Kai Chiu, Andreas P. Schnyder, Phys. Rev. B 90, 205136 (2014).
 Y. X. Zhao, Andreas P. Schnyder, Z. D. Wang, Phys. Rev. Lett. 116, 156402 (2016).
 Y.-H. Chan, Ching-Kai Chiu, M. Y. Chou, A. P. Schnyder, Phys. Rev. B 93, 205132 (2016).
 Ching-Kai Chiu, Y.-H. Chan, Xiao Li, Y. Nohara, A. P. Schnyder , arXiv:1606.03456 (submitted).