Wavelet Poisson solver - Huge change in total energy when increasing the plane-wave cut-off energy from 1200 to 1260 Ry

[Torstein Fjermestad]

Dear all, 

As part of a basis set convergence test, I gradually increase the plane wave basis set cut-off energy. The atomic system is a cluster model of methanol adsorbed in a zeolite. I isolate the system from its neighboring unit cells by using the wavelet Poisson solver. 

I use a cubic box of 30 Å. The size of the system is about 21 Å in the longest direction. The atom-centered basis set is TZV2P. 

When I increase the cut-off from 900 Ry to 1200 Ry, the total energy varies in a range less than 5 kJ/mol. However, when I increase the cut-off from 1200 Ry to 1260 Ry, the total energy is after  6 SCF iterations  1.38E+07 kJ/mol lower! 

Because of the massively different total energy, I stopped the calculation.   

I have attached the output files of the two calculations. The complete input can be found at the start of the output files. 

What could be the cause of this behavior? 

Thank you very much for your help. 

Please tell me if you need more information to understand the problem better.

Best regards,

Torstein Fjermestad

 

[Frederick Stein]

Dear Torstein,

You not only need to adjust the CUTOFF but also EPS_DEFAULT (and if set explicitly the other thresholds) in the QS section. How did you obtain the input file? I would never set all parameters. Especially EPS_DEFAULT sets a variety of other parameters if these are not set explicitly.

Best,

Frederick