2012/1/15 jiayudai <daijiayu at nudt.edu.cn>: > > Dear Axel and Yun-Peng, > > Thanks for your physial translation. Now, i think i can understand the > physical figures in this problem. As axel said, the forces can be correct, > but the energies are wrong. However, what i want to get is the pressure from > positive ions. Thus, i should need the correct energies at first. For the > treatment of Coulomb interations, we usually do the summation within a > cutoff of a distance if we only use the formation of 1/r. This is an > approach but it can solve the problem of divergence. Therefore, i think we
this is not *solving* the problem, it is *ignoring* it. and much worse. since coulomb interactions are so very long-range, a cutoff will induce *massive* fluctuations of properties like pressure relative to the choice of cutoff (and what kind of cutoff, spherical? or use the minimum image cell?) and that already for a neutral system. i suggest you set up a classical simple test case with a simle rocksalt like crystal structure and check out how much the pressure depends on the choice of cutoff with and without ewald summation. i am certain, this will change your mind and you will be shocked. axel. > can change the ewald formula in DFT using 1/r (with a cutoff). Is it? > -- Dr. Axel Kohlmeyer akohlmey at gmail.com ?http://goo.gl/1wk0 College of Science and Technology Temple University, Philadelphia PA, USA.
