aksonik

Hi Enthalpy - thank you for raplay. I know the positions and charges of all ions in the crystal. If I want to sum up the contributions of individual ions I have to decide which take into consideration and which don't - amount of them is infinite, so ions in a long distance have to be neglected. Single unit cell contain equal number of positive and negative ions. That is why I intend to consider only integer amount of them. I suppose, this is what you meant writing "couple in pairs". Best regards, Aksonik

Thank you for replay. If I consider uniformly charged infinite disc, lines of electric field are perpendicular to it. Then, I can use any symmetrical Gaussian surface and find out that electric field doesn't depend on distance. Now, If I treated my crystal as a set of parallel, infinite and charged uniformly, positively and nagatively discs arranged alternatelyelectric field outside would be zero - that is okay. The thing is, a point very close to the surface doesn't "see" nearest part of the crystal as uniformly charged. I expect differences in electric field depending on positions in the surface plane - in the same distance but above positive or negative ion. I wonder, is a reason why I should differently consider ions in the surface plane then in deep (cylindrically), not uniformly in all directions (spherically)? Best regards, Aksonik

I intend to calculate electric field in certain point above surface of crystal, which is infinite in directions of surface and below. Crystal is composed of unit cells containing equal amount of positive and negative ions (+1e and -1e). Distances between ions and between point and surface (jons at the top) are in the same order of magnitude. Should I simply calculate electric field from ions containing in some radii of the point - like from half of a spheres, and extrapolate results to infinity? Or mayby consider some thin discs or whatever else making use of Gauss's Law? Best regards, Aksonik