2.2. Calculational details
All of the calculations are carried out using plane-wave pseudopotential
DFT+U method in “CASTEP” module, which is developed by Accelrys
Company[21], the exchange correlation energy were
treated based on the GGA with PBE functional[22],
with the considerations of spin-orbit polarization. In the simulation,
the core electrons were treated with the ultrasoft pseudopotential, and
the configurations of valence electrons were selected as Bi
6s26p3, O
2s22p4, Br
4s24p5, Sc
3d14s2, Ti
3d24s2, V
3d34s2, Cr
3d54s1, Mn
3d54s2, Fe
3d64s2, Co
3d74s2, Ni
3d84s2, Cu
3d104s1, Zn
3d104s2. The plane-wave cut-off
energy of 500 eV and a Monkhorst-Pack 3×3×3 \(k\)-point grid were used.
In addition, the convergence standards were set as the follows: the
force and stress were less than 0.5 eV/Å and 0.1 Gpa, respectively as
well as the energy change was less than 2 × 10−5eV/atom[18]. More importantly, we adopted DFT+U
approach to overcome the disadvantage of GGA-PBE due to the
nonnegligible d-d transition of transition metal[23,
24]. As we all know, a finite onsite Coulomb interaction is essential
for accurately describing atoms containing d
electrons[25], so the on-site Coulomb interaction
with U=4.0 eV is used in the calculations[26]. In
order to make the calculated optical properties results consistent with
the actual situation, “scissors operators”
technology[27]was adopted, and the correction
factor was set as 0.8 eV in our work, which is based on the deviation of
the calculated values and the experimental data of average band gap.