Various CutOff's and their default values

[neumannrf]

Hi everyone!

The RASPA documentation does not mention CutOff, even though that is the most common cut-off radius used in the input files in the Examples folder.

• What does 'CutOff' mean?
• Are there cut-off radius parameters that no default value, i.e. the have to be defined every time?
• What are the default values of each 'CutOff____' parameter?

Having this in the documentation could avoid overspecification in the input file.

[Christopher]

Hi!

in the raspa.pdf you can find some information about cutoffs on page 18. General information about the cutoff radius can be found in any molecular simulation book e.g. Frenkel and Smit. Cutoff means that the potential is only considered up to a certain value of radius.

In raspa for every cutoff value there are defaults, but you should really take care of the cutoff radius yourself because they should be considered as a part of your forcefield. If you use a different cutoff than you will probably receive different results!

You can get default values from the output file of your simulation (if you don't set any value for cutoffs). You get:
CutOff VDW : 14.000000 (196.000000)
CutOff VDW switching on: 12.600000 (158.760000)
CutOff charge-charge : 14.000000 (196.000000)
CutOff charge-charge switching on: 9.100000 (82.810000)
CutOff charge-bonddipole : 12.000000 (144.000000)
CutOff charge-bondipole switching on: 8.400000 (70.560000)
CutOff bonddipole-bonddipole : 12.000000 (144.000000)
CutOff bonddipole-bondipole switching on: 9.000000 (81.000000)

It's always a good idea to check your input with the output file.

Best Christopher

[neumannrf]

Dear Christopher,

I went to the code and tried to find where those values you cited are defined, but I failed. What I found indicated different values, as in

• CutOffVDW = 12 https://github.com/iRASPA/RASPA2/blob/master/src/input.c#L386
• CutOffChargeCharge = 12 https://github.com/iRASPA/RASPA2/blob/master/src/input.c#L797

While some of the other cut-off radii are defined as fractions of these two parameters.

Are we maybe using different versions of the software? I am looking at the latest version as available in the repository.

[Christopher]

Hi again,

oh sorry - seems like i mixed something up - default values are

 CutOff VDW : 12.000000 (144.000000)
 CutOff VDW switching on: 10.800000 (116.640000)
 CutOff charge-charge : 12.000000 (144.000000)
 CutOff charge-charge switching on: 7.800000 (60.840000)
 CutOff charge-bonddipole : 12.000000 (144.000000)
 CutOff charge-bondipole switching on: 8.400000 (70.560000)
 CutOff bonddipole-bonddipole : 12.000000 (144.000000)
 CutOff bonddipole-bondipole switching on: 9.000000 (81.000000)
 
This is from version 2.0.38