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xiao_ma523

铁杆木虫 (著名写手)

[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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953623702

金虫 (小有名气)

【答案】应助回帖

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franch: 金币+2, 谢谢回帖交流,, 2013-04-15 21:38:42
用GGA-PBE交换相关泛函时,SCF 中应该选Density mixing 吧,除非你用的是杂化泛函,如PBE0.如果不是算金属,你的K点取的太大了,SCF tolerance又太小了。还有迭代次数也太少了,有的100次是不能收敛的,建议调到300或500.
9楼2013-04-15 08:59:02
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xw2008

铜虫 (小有名气)

【答案】应助回帖


感谢参与,应助指数 +1
liliangfang: 金币+1, 谢谢交流 2013-01-26 15:22:31
k-points:20×20×20设的挺多的 你算的是什么材料啊?最好有把生成的.castep文件,才好判断。
Max. SCF sysles先把设大点,试试。
2楼2013-01-25 13:34:52
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zhoupeng87

版主 (文学泰斗)

优秀版主优秀版主

【答案】应助回帖

感谢参与,应助指数 +1
。。。。。你这个怎么整的这么复杂的
3楼2013-01-25 14:17:29
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xiao_ma523

铁杆木虫 (著名写手)

引用回帖:
2楼: Originally posted by xw2008 at 2013-01-25 13:34:52
k-points:20×20×20设的挺多的 你算的是什么材料啊?最好有把生成的.castep文件,才好判断。
Max. SCF sysles先把设大点,试试。

上边的问题就是在.castep里边截出来的。。。算的是Ti基多元固溶体,采用的是虚晶近似。我试一下,可是Max. SCF cycles要调高多少比较好呢。。。
4楼2013-01-25 14:19:51
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