Dear SIESTA users: I used dzp atomic basis,160 ry meshcutoff ,30 Bohr kgrid cutoff to calculate FePt system(see the pictures of my unit cell in attachment), however, it seems to take forever to converge with the SCF cycle. dDMax(around 1.0) stays far beyond tolerence (0.00001), and if I increase the cell to 108 atom unit cell(3x3x3 supercell), dDmax becomes even larger. Yet the simplest unit cell with 4 atoms converges fine.
I also used szp atomic basis,spin polarized and larger cutoff(300 ry meshcutoff,40 Bohr kgrid cutoff ) with 32 atom cell, the problem is still the same, it seems to have nothing to do with the cutoff I choose. Could anyone give me a clue where the problem might lie? I would really appericiate your help. If it doesn't converge, the forces and stress are wrong and so is the later MD steps. Here is a fragment of my SCF cycle: siesta: 42 -25183.5213 -24873.4575 -24873.4883 1.2337 -2.1597 siesta: 43 -25153.3555 -24872.5874 -24872.6213 1.0953 -1.7754 siesta: 44 -25204.6434 -24870.7750 -24870.8201 1.0794 -2.1741 siesta: 45 -25174.8238 -24868.9171 -24868.9419 1.3392 -2.3371 siesta: 46 -25138.7377 -24868.4595 -24868.4879 1.0200 -2.1080 siesta: 47 -25177.5378 -24866.3887 -24866.4199 1.1245 -1.9894 siesta: 48 -25159.6251 -24865.8291 -24865.8733 1.0482 -2.0247 siesta: 49 -25206.9572 -24864.1873 -24864.2264 1.0436 -2.1378 I attached the output file and pictures of the unit cell I used. Generally speaking, the atomic position is the same as FCC crystal, only that a=b,c=0.95a, because of the ordering alignment of Fe and Pt ( a layer of Fe then a layer of Pt along the c-axis) SuiYang 2006-12-05
FePtsuper2.out
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