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

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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

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Total electrostatic energy = 1.551673825736E+05 kJ/mol

run 2

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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.

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