Hi, My question is, is the R point of the 12 atoms unit cell equivalent to the Gamma point of 432 atoms unit cell? The band gap should be estimated from density of states. Of course, because of the finite number of k-points in practice and finite smearing, the band gap estimated from density of states is usually not precise. The most accurate method to determine the band gap is to plot the band structure along symmetric paths. hope it helps Yun-Peng
--------------------------------------------------------Yun-Peng WangPostdoctoral AssociateDepartment of Physics and theQuantum Theory ProjectUniversity of [email protected] Date: Tue, 20 Aug 2013 21:50:02 -0400 From: [email protected] To: [email protected] Subject: [SIESTA-L] Bizarre behaviour Dear Siesta users, I'm having very bizarre problem.I'm simulating the primitive cubic unit cell(12 atoms) of the CH3N3SnI3 perovksite with GGA and PBE and gives me band gap of Eg=0.9 eV at R point with 8x8x8 Moshkrof automatic k sampling(i know it's wrong in DFT, but still) and then i use supercell approach built in with 3x3x3 unit cell(432 atoms) with Gamma point only and i get a bangap of 1.6 eV. I've checked against plane cutoff convergence seems ok. I thought maybe dispersion is too big so one should sample it more finely, but it turns out meff=0.13me, which should be fine. Any ideas ? With Best Regards, Andrei Buin.
