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xiao_ma523

铁杆木虫 (著名写手)

应助: 2 (幼儿园)
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虫号: 1485289
注册: 2011-11-10
专业: 粉末冶金与粉体工程

[求助] MS中CASTEP计算结构优化时不收敛问题，请各位指教。。。

刚开始学习使用 ms castep ，小白一只，在进行结构优化计算的时候，出现如下问题，烦请各位前辈们指教。。。。谢谢。。。
（计算函数选取为GGA-PBE；计算参数选择分别为：k-points：20×20×20；SCF设置：SCF tolerance：5.0e-7eV/atom，Max. SCF sysles: 100，Electronic minimizer：All B ands/EDFT
http://）

------------------------------------------------------------------------ <-- SCF
SCF loop    Energy          Fermi          Energy gain    Timer <-- SCF
                           energy       per atom       (sec) <-- SCF
------------------------------------------------------------------------ <-- SCF
Initial  -1.05658475E+003  4.29446436E+001                      40.51  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   1  -1.66908169E+003  2.06199975E+001 3.06248473E+002    201.90  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   2  -1.71727432E+003  1.54132235E+001 2.40963134E+001    368.41  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   3  -1.73512023E+003  1.31966544E+001 8.92295366E+000    505.40  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   4  -1.74004485E+003  1.24138206E+001 2.46230895E+000    636.64  <-- SCF
   5  -1.74135250E+003  1.21899463E+001 6.53828871E-001    773.64  <-- SCF
   6  -1.74205719E+003  1.20787843E+001 3.52340973E-001    907.32  <-- SCF
   7  -1.74259344E+003  1.19953030E+001 2.68127227E-001 1037.62  <-- SCF
   8  -1.74306614E+003  1.19286041E+001 2.36350991E-001 1177.77  <-- SCF
   9  -1.74358796E+003  1.18488409E+001 2.60909149E-001 1298.85  <-- SCF
   10  -1.74403744E+003  1.17938519E+001 2.24738643E-001 1421.06  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   11  -1.74455876E+003  1.17365970E+001 2.60662432E-001 1547.33  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   12  -1.74497637E+003  1.16890613E+001 2.08802683E-001 1672.85  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   13  -1.74535476E+003  1.16477635E+001 1.89198766E-001 1784.51  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   14  -1.74569639E+003  1.16017743E+001 1.70815013E-001 1896.44  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   15  -1.74603497E+003  1.15495874E+001 1.69286593E-001 2027.35  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   16  -1.74633929E+003  1.15088101E+001 1.52159230E-001 2140.21  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   17  -1.74664029E+003  1.14673428E+001 1.50503130E-001 2250.68  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   18  -1.74691967E+003  1.14291301E+001 1.39687296E-001 2383.77  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   19  -1.74716002E+003  1.13983485E+001 1.20175874E-001 2524.37  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   20  -1.74738725E+003  1.13643370E+001 1.13616354E-001 2637.47  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   21  -1.74764344E+003  1.13346137E+001 1.28091921E-001 2761.41  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   22  -1.74783115E+003  1.13112076E+001 9.38565737E-002 2880.58  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   23  -1.74801534E+003  1.12912355E+001 9.20978199E-002 3019.49  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
   24  -1.74815772E+003  1.12827309E+001 7.11860533E-002 3166.94  <-- SCF
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* predicted gradient is positive
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016
*Warning* predicted gradient is positive
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016
   25  -1.74831435E+003  1.12683472E+001 7.83167816E-002 3295.82  <-- SCF
*Warning* predicted gradient is positive
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016
*Warning* predicted gradient is positive
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016
*Warning* predicted gradient is positive
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016
*Warning* predicted gradient is positive
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016
*Warning* predicted gradient is positive
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016
   26  -1.74846036E+003  1.12568548E+001 7.30063648E-002 3429.77  <-- SCF
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016
   27  -1.74859810E+003  1.12399413E+001 6.88709270E-002 3565.08  <-- SCF
   28  -1.74872556E+003  1.12249860E+001 6.37300369E-002 3706.03  <-- SCF
   29  -1.74883372E+003  1.12156147E+001 5.40795198E-002 3822.78  <-- SCF
*Warning* predicted gradient is positive

主要问题就是两个warning怎么才能解决：
*Warning* predicted gradient is positive
*Warning* step too small in line minimisation; setting to
  2.220446049250313E-016

[ Last edited by xiao_ma523 on 2013-1-25 at 10:22 ]

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