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howto:troubleshooting [2021/01/25 11:28] Xavier Gonzehowto:troubleshooting [2021/07/12 15:28] (current) – [Troubleshooting] Jean-Michel Beuken
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 In this page, the user will find tips to fix several problems with ABINIT.    In this page, the user will find tips to fix several problems with ABINIT.   
  
-Many other tips might be found on the [[https://forum.abinit.org|forum]], or in the [[https://docs.abinit.org|standard ABINIT documentation]].+Many other tips might be found on the [[https://discourse.abinit.org|forum]], or in the [[https://docs.abinit.org|standard ABINIT documentation]].
  
  
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 If you think to have obtained all information that ABINIT was supposed to give you, try to identify whether ABINIT stops because of geometry optimization problem or SCF problem. In the first case, your input geometry is perhaps crazy. Anyhow, see the next items in this troubleshooting page. If you think to have obtained all information that ABINIT was supposed to give you, try to identify whether ABINIT stops because of geometry optimization problem or SCF problem. In the first case, your input geometry is perhaps crazy. Anyhow, see the next items in this troubleshooting page.
 +
 +By the way, there might also be memory problems ... See <https://docs.abinit.org/topics/TuningSpeedMem>.
 +
  
 ==== Incorrect initial geometry ==== ==== Incorrect initial geometry ====
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 ==== SCF cycle does not converge ==== ==== SCF cycle does not converge ====
  
-The default algorithms for SCF (see input variable iscf) are an excellent compromise between speed and robustness (see e.g. +The default ABINIT algorithm for SCF (see input variable iscf) is an excellent compromise between speed and robustness
 +It is referred to as Pulay II in Fig. 10 of 
 +N. D. Woods and M. C. Payne and P. J. Hasnip, J. Phys.: Condens. Matter 31, 453001 (2019), and appear on the Pareto frontier. 
 +Some parameters in the Kerker preconditioning have also an effect on the balance between speed and robustness, and the ABINIT default values 
 +are good for metallic systems. As thouroughly discussed in this reference, there is no fool-proof fast algorithm. 
 + 
 +If your SCF cycle do not converge (see nres2 or vres2 column in the output file), the reasons can be: 
 +(1) Insufficient underlying accuracy in the solution of the Schrödinger at fixed potential 
 +(2) Transient non-linear behaviour of the SCF, due either to (2a) sudden change of occupation numbers (usually only for metals), or (2b) long-wavelength fluctuations of potential, bigger than the gap. 
 + 
 +Start first to address (2), by some tuning which can come without significantly slowing ABINIT. Test different values of diemac. The default is very large, and suitable fo metals. Try running with a small value (perhaps 5) if your system is a bulk semiconductor or a molecule. If it is a doped solid, some intermediate value (perhaps 50) might be appropriate. 
 + 
 +If this does not work, try to address (1), set tolrde to 0.001, increase the value of nline (e.g. 6 or 8 instead of the default 4), as well as of nnsclo (e.g. 2 instead of the default). Your residm should be significantly lower than without such modifications, and perhaps your problem will be solved. 
 + 
 +If this still does not work, but your residm did not look bad after all before addressing (1), then revert back to the default values of tolrde, nline an nnsclo, as this indeed slows down ABINIT. 
 + 
 +Then, try to use iscf 2. This is a very slow but inconditionally convergent algorithm provided diemix is small enough. At some stage of convergence, you might restart with the obtained _DEN a better algorithm, as non-linear effects should have been eliminated at some stage. 
  
 ==== Geometry optimization does not converge ==== ==== Geometry optimization does not converge ====
howto/troubleshooting.1611570533.txt.gz · Last modified: 2021/01/25 11:28 by Xavier Gonze