The numerical precision of the calculations depends on many settings, among which the precision in solving the Kohn-Sham self-consistent equation.
Several parameters govern the SCF loop. The maximum number of cycles is given by nstep, but the iterative procedure might be stopped earlier, as soon as the criterion chosen by the user is fulfilled. The user is asked to give a tolerance on some measure of the convergence. The user must choose among toldfe, toldff, tolrff, tolvrs and tolwfr.
Some input variables relate to the solution of the Schrödinger equation. However, usually the related iterative techniques are well-tuned, so that these input variables (nline and tolrde) are usually used only by experts. However, in cases where the convergence is difficult, it might be interesting to test improving them, as well as modifying nnsclo.
The accuracy variable enables to tune the accuracy of a calculation by setting automatically up to seventeen variables.
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Basic input variables:
... accuracy [ACCURACY]
... nstep [Number of (non-)self-consistent field STEPS]
... toldfe [TOLerance on the DiFference of total Energy]
... toldff [TOLerance on the DiFference of Forces]
... tolrff [TOLerance on the Relative diFference of Forces]
... tolvrs [TOLerance on the potential V(r) ReSidual]
... tolwfr [TOLerance on WaveFunction squared Residual]
Useful input variables:
... nbdbuf [Number of BanDs for the BUFfer]
Input variables for experts:
... nline [Number of LINE minimisations]
... nnsclo [Number of Non-Self Consistent LOops]
... tolrde [TOLerance on the Relative Difference of Eigenenergies]
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