Hi,

I've tried to calculate the electrostatic properties of the same system (protein in water and salt) twice, using essentially the same settings except for the grid dimensions and number of points, as follows:

run 1
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  Grid dimensions: 161 x 161 x 161
  Grid spacings: 0.400 x 0.400 x 0.400
  Grid lengths: 64.000 x 64.000 x 64.000
  Grid center: (9.745, 12.641, 21.402)

run 2
----

  Grid dimensions: 193 x 193 x 193
  Grid spacings: 0.333 x 0.333 x 0.333
  Grid lengths: 64.000 x 64.000 x 64.000
  Grid center: (9.745, 12.641, 21.402)

The largest dimension of protein is 42 angstroms.

Now as far as I understand it, I should expect that the results of run 1 shouldn't be too different than the results of run2. However, what I got was:

run 1
----
Total electrostatic energy = 1.551673825736E+05 kJ/mol

run 2
----
Total electrostatic energy = 2.042898691098E+05 kJ/mol

Am I missing something? Does the number of levels have an influence on the energy results? Or should I expect better convergence when the grid is smaller?

Thank you,
Ran.
 

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Ran Friedman
Laser laboratory for fast reactions in biology
Department of biochemistry
Faculty of life sciences
Tel-Aviv university
972-3-6409824
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