periodicity

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 — periodicity [2014/02/09 14:50] (current)oschuett converted from doc/tutorialCp2k.html, Credit: Fawzi Mohamed 2014/02/09 14:50 oschuett converted from doc/tutorialCp2k.html, Credit: Fawzi Mohamed 2014/02/09 14:50 oschuett converted from doc/tutorialCp2k.html, Credit: Fawzi Mohamed Line 1: Line 1: + ​This text is probably out of date and needs to be revised.​ + + ====== Periodicity ====== + The Cp2k program is optimized for periodic calculations,​ and those are the default, still it is possible to perform also other kinds of calculations. First an important thing to note is that by convention the cell goes from 0 to h, not from -h/2 to h/2, thus if you want to put a cluster at the center of the cell you need to put it in h/2 not in 0. + + The periodicity of the neighbor list, and thus of the gaussian collocation/​integration is controlled by ''​FORCE_EVAL%SUBSYS%CELL%PERIODIC''​. + + The poisson solver (electrostatics) is controlled in the section + ''​FORCE_EVAL%DFT%POISSON''​. The possible poisson solver are chosen with the ''​POISSON_SOLVER''​ keyword, that can have the values ​ + + * ''​PERIODIC'',​ which can do only fully periodic solvers, + * ''​ANALYTIC''​ which can do 0, 1d and 2d periodic solutions using analytical green functions in the g space (slow convergence),​ + * ''​MT''​ Martyna Tuckermann decoupling, that interacts only with the nearest neighbor, beware these are completely wrong in the cell is smaller than twice the cluster size (with electronic density), + * ''​MULTIPOLE'',​ uses a schema that fits the total charge with one gaussian per atom + + The periodicity of the poisson solver (electrostatics) is set in ''​FORCE_EVAL%DFT%POISSON%PERIODIC'',​ and the poisson solver chosen should support it.