Dear Siesta users, I have been trying to optimize a 32 atom 2D supercell of Germanium Carbide. For that I am trying to test the convergence of my system with respect to the k-mesh value. Following according to the siesta hands on tutorial, I have run optimization of the system with k-mesh value starting from 4x4x1 up to 30x30x1. Now even though the lattice parameter has obtained a constant value from 20x20x1 k-mesh, the free energy values are fluctuating very much, even near 30x30x1 k-mesh. I am attaching a data file listing the k-mesh used and the corresponding free energies, lattice parameters and pressures. #k free_energy(eV) a(Ang) press(kBar) #---------------------------------------------------
4 -4404.686569 13.071919 1.58775270 5 -4404.692009 13.071926 1.57574542 6 -4404.683644 13.071920 1.58159257 7 -4404.690383 13.071918 1.58333081 8 -4404.690468 13.071920 1.58158769 9 -4404.656950 13.071918 1.58728229 10 -4404.689479 13.071920 1.58758950 11 -4404.651242 13.071923 1.55663793 12 -4404.652430 13.071924 1.55242216 13 -4404.652785 13.071924 1.55406592 14 -4404.690453 13.071917 1.58822447 15 -4404.690326 13.071920 1.58736858 16 -4404.648946 13.071924 1.58553524 17 -4404.690409 13.071919 1.58581311 18 -4404.656695 13.071924 1.51914825 19 -4404.647953 13.071923 1.56108155 20 -4404.656823 13.071924 1.51265983 21 -4404.662298 13.071924 1.56920158 22 -4404.660099 13.071925 1.57130732 23 -4404.654394 13.071924 1.52465516 24 -4404.666235 13.071924 1.56528804 25 -4404.655273 13.071924 1.51864296 26 -4404.654969 13.071924 1.57698239 27 -4404.654026 13.071924 1.51899044 28 -4404.660686 13.071924 1.57076477 29 -4404.647965 13.071924 1.58495969 30 -4404.650918 13.071924 1.58155660 I have been optimizing the above structure with spin-polarization turned ON. Is it the reason why the free energy values are not reaching a converged value? Should I carry out the convergence tests with spin-polarization option turned off and turn it on only while calculating bands, DOS and other properties? Please help me in this regard. Thank YOu in advance. Sunetra Das
