Within all relaxation algorithms (IBRION=1,2 and 3) the parameter POTIM should be supplied in the INCAR file. For IBRION0, the forces are scaled internally before calling the minimization routine. Therefore for relaxations, POTIM has no physical meaning and serves only as a scaling factor. For many systems, the optimal POTIM is around 0.5. Because the Quasi-Newton algorithm and the damped algorithms are sensitive to the choice of this parameter, use IBRION=2, if you are not sure how large the optimal POTIM is.

SYSTEM = Mg-hex
ENCUT = 250
ISTART = 0; ICHARG = 2
ISMEAR = 1; SIGMA = 0.2
NSW = 60; IBRION = 2
ISIF = 3
POTIM = 0.2
EDIFF = 1E-6; EDIFFG = -1E-3
PREC = Accurate

Originally posted by stractor at 2010-12-18 10:52:01:
我一般使用默认值POTIM=0.5。而且IBRION=2的算法比较可信。
驰豫的时候POTIM的设置只会影响运行的效率，不会对结果又明显的影响。
不用管它，默认值很不错。

[ Last edited by stractor on 2010-12-18 at 1 ...

Originally posted by swx0789 at 2010-12-23 08:24:33:
我现在也在优化晶体的结构参数。看了后博士的中文入门手册，虽然讲的很详细，当有个地方还不是很明白。就他例子的关于Mg的晶格参数的优化（P25）。
我取10个点，循环完后，拟合得到最佳的a值。他后面说“在该体积 ...

Originally posted by valenhou001 at 2010-12-23 18:47:48:


“改变$i的循环值，再运行run_cell计算一次”
此时$i只附了一个值，就是前面由EOS拟合得到的平衡体积V_0计算(V_0 = 0.5*sqrt(3.0) a^3 * c/a,  c/a的值取自run_cell所设置的，即c/a的值与前一步中run_cell中 ...

6楼: Originally posted by valenhou001 at 2010-12-23 18:47:48
“改变$i的循环值，再运行run_cell计算一次”
此时$i只附了一个值，就是前面由EOS拟合得到的平衡体积V_0计算(V_0 = 0.5*sqrt(3.0) a^3 * c/a,  c/a的值取自run_cell所设置的，即c/a的值与前一步中run_cell中的 ...