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abcasi金虫 (小有名气)
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【讨论】VASP计算问题fatal internal in brackting
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VASP计算问题fatal internal in brackting 我在用VASP进行结构优化时，output里最后出现 this message says that during geometry optimisation no reasonable next step could be found with Brent's algorithm (linear bisectioning) please check the following 1) is the system converged already? (look at the forces in OUTCAR, especially if you use the total energy change as congvergence criterium for ionic optimisation) 2) if not: is each ionic step converged electronically ( this is needed to obtain reasonable forces) 官网上的回答，大意是说系统认为计算已经收敛了没有必要再算下去了。 然后又问： Well, I encounter the same problem when I optimize the geometry. I set EDIFFG=-1E-2. And every SCF is converged. But in the last SCF non-local-force acting on ions is -.178E-14 0.000E+00 0.000E+00; it seems not small enough,right? I see the total drift is 0.000063 -0.000007 -0.000005. I don't know whether the optimization is OK ended. Or what parameter do I need to let the convergence continue? 大意是说他又算了一次，又出了同样的错误。而且他看到计算结果中最后一步的力已经很小了，但是不知道是不是已经收敛了。 版主回答说： sometimes, if the calculation is already highly converged, vasp cannot interpolate the next step to within the numerical accuracy because it simply would be so small. (this behaviour is machine-dependent). If you have used IBRION=2, it may help to switch to IBRION=1 and set ADDGRID=.true. in addition 大意是说让他不要再用ＣＧ方法了，改用速降法再算算 另外还有人提问了类似的问题： After 20 ionic steps, the surface relaxation calculation is automatically stopped. Error massage is attached as below: 20 F= -.68277137E+02 E0= -.68272811E+02 d E =-.140470E-01 mag= 11.1515 curvature: 0.00 expect dE= 0.219-310 dE for cont linesearch 0.213-310 ZBRENT: fatal internal in brackting system-shutdown; contact gK immediately what really happened? Anybody encounted the same problem before? 大意是说算了几个离子步后系统自动停了。 版主的回答是： This error occurs if the next ionic step cannot be estimated with the ZBRENT algorithm (the algorithm is documented in the Numerical Recipies). --) you seem to be at the energy minimum of the parabola already (curvature=0.00,....): For most applications a geometry can be regarded as converged if the maximum remaining forces are less than 0.01 eV/AA, therefore EDIFFG = -1e-02 is a reasonable choice. Please check the forces of your last ionic step (in OUTCAR) --) Please also have a look at the XDATCAR file: If the ionic step sizes have become very small already, the GC algorithm may fail to extrapolate the next step (---> switch to IBRION = 1 instead) --) If you want to increase the accuracy of the calculated forces even more, set ADDGRID = .True. in INCAR 大意也是说下一步算不起来了，已经能量最低了或者已经达到收敛标准了，如果想算下去就提高精度。 |
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