First-principles calculations are performed within the density functional theory (DFT) for the CaCO3 vaterite polyrnorph considering exchange-correlation potentials in the local density approximation (LDA) and generalized gradient approximation (GGA). The crystal structure of vaterite is considered to be orthorhombic, although there is considerable debate in the literature about a possible hexagonal cell with disordered carbon and oxygen atoms. After convergence, the calculated orthorhombic lattice parameters are demonstrated to be in good agreement with experimental results. The direct energy gap for vaterite is preview to be wide and estimated in LDA and GGA to be E-G(Gamma-Gamma)(LDA) = 4.68 eV and E-G(Gamma-Gamma)(GGA) = 5.07 eV, but should underestimate the actual value yet to be measured. The optical absorption intensity is previewed to be relevant for energies larger than 6.2 eV. (c) 2007 Elsevier B.V. All rights reserved.