Lattice dynamics and pressure induced metallization of solid iodanil (C₆I₄O₂) studied using density functional theory

A detailed ab initio study addressing the structural, lattice dynamics and pressure induced metallization has been carried out for solid iodanil (C6I4O2). The computed ground state structural properties reveal the crucial role of considering van der Waals correction in determining these properties. An excellent agreement can be noticed between our computed zone centered phonon frequencies and experimentally reported results. Though computed phonon dispersion confirms the dynamical stability of solid iodanil in the P2 ( 1 )/c symmetry, a softening of the transverse acoustic phonon mode can be observed with pressure along the D-B direction. At 22 GPa, i.e. across insulator-metal transition, the TA branch along D-B directions hardened, where the role of optical phonon mode (A( u )) is prominent. In addition, the elastic constants were also calculated to ascertain the mechanical stability of the solid iodanil. Moreover, the electronic band structure has been calculated using the quasiparticle G W- 0 (0) approximation which results in a band gap of 2.49 eV. This value is significantly larger than the value obtained by the generalized gradient approximation, thus emphasizing the importance of quasiparticle correction in solid iodanil. This study clearly shows a reduction of the band gap under pressure and hence result in a band overlap eventually driving iodanil to metallize around 22 GPa. The pressure variation of the inter- and intramolecular bond lengths as well as the charge density plots explain the significant role of the intermolecular I-I distance in understanding the metallization of solid iodanil.