Calculation of the effective interaction parameter in the LDA + U method by a linear response approach for Fe ( OH ) 2

In this paper we have investigated the electronic properties of $\text{Fe}{(\text{OH})}_{2}$ hydroxide by using the spin-polarized version of the generalized gradient approximation $(\ensuremath{\sigma}\text{-GGA})$ as well as the $\ensuremath{\sigma}\text{-GGA}+U$. Our calculations for the iron hydroxide show that the $\ensuremath{\sigma}\text{-GGA}$ results are at variance with experimental findings. On the other hand, we have shown that $\ensuremath{\sigma}\text{-GGA}+U$ is capable of opening a gap at the Fermi level resulting in an insulating ground state. Moreover, the frequencies of the Raman-active ${\text{A}}_{1g}(\text{OH})$ and infrared-active ${\text{A}}_{2u}(\text{OH})$ stretching modes of OH group are calculated at ambient conditions. We have found the calculated gap as well as the calculated frequencies are in good agreement with experimental results.