[ESPResSo-users] iccp3m question

[Xikai Jiang]

Dear All:

I'm testing iccp3m for a system that consists of a single charged particle confined between two parallel walls with zero electrical potential difference in Espresso-3.3.0. All atoms are fixed in space, and the charged particle carries a charge of 50e. My purpose is to test whether the system is electrically neutral (it should be neutral in principle).

When I put the test charge 0.2nm above the bottom wall, and run Espresso for 1 step using 1 core, the net charge of system is 0.2717e, which can be considered neutral. But when I run the same simulation using 8 cores, the net charge of system becomes 6.224e, and cannot be considered neutral within numerical inaccuracy.

I tried to put the test charge away from the wall (1nm away), the net charge in system becomes 4.9e using both 1 core and 8 cores. Refining the grid on wall (spacing from 0.3nm to 0.1nm) helps to reduce the net charge in system to 2.4e, about 4.8% of the amount of the test charge.

Does anyone have ideas where the problem is? I have attached the test code, any help or comments are appreciated.

Regards.

Xikai

test_constant_potential_parallel_plate_nve_fixed_atoms.tcl
Description: Tcl script