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--- models:openkim [2019/02/23 09:55] – created daniel
+++ models:openkim [2019/03/06 18:59] (current) – daniel
@@ Line 3: / Line 3: @@
 ----
-Analytic potentials use the parameters $\alpha_i$ as arguments to analytic function templates.
+//potfit// supports the [[https://openkim.org/|OpenKIM]] framework for defining atomic interactions. It is possible to use any OpenKIM model which publishes its parameters. Unfortunately it is currently not possible to check if a model does this on the web interface. //potfit// provides a small utility called [[utilities:kim_read_model_props]] which probes a model for supported features.
-A well-known example for this would be the Lennard-Jones potential, which uses two parameters $\epsilon$ and $\sigma$ to define a potential:
-$$V(r)=4\varepsilon\left[\left(\frac{\sigma}{r}\right)^{12}-\left(\frac{\sigma}{r}\right)^{6}\right]$$
+== Building potfit with OpenKIM support ==
-{{ :analytic.png?300 }}
+The //potfit// build system should be able to pick up the location of the OpenKIM libraries on your system and use them automatically. Just use ''kim'' for the model switch in the configure command:
-Using an analytic form for $V(r)$ allows to define the atomic interaction for all possible distances between atoms with very few parameters compared to tabulated potentials. The problem of local parameters (see [[tabulated|Tabulated potentials]]) is also not present, parameters are usually global parameters. In certain cases it is even possible to attribute some physical meaning to individual parameters.
+<code>./waf configure -m kim</code>
-The analytic potential implementation in //potfit// has additional features which are only useful with this kind of interactions. They are described on the [[potfiles::format0|analytic format]] page.
+The interaction switch is disabled for OpenKIM.
+== Additional parameters  ==
+Enabling support for OpenKIM also requires additional settings in the parameter file. The most important one
+is the model name in "kim_model_name". This corresponds to the Extended KIM ID from the OpenKIM website, e.g. "EAM_CubicNaturalSpline_AngeloMoody_1995_Ni__MO_800536961967_002".
+To provide some assistance in creating a potential file for an unknown OpenKIM model there is the
+"kim_model_param" setting. It can be used to get a potential file template. The possible values are:
+  * dump_file
+  * dump
+  * use_default
+Using "dump_file" will create a //potfit// potential for the selected "kim_model_name". "dump" will output a //potfit// potential to standard output. And using "use_default" will use the default values for all parameters as provided by the OpenKIM model.
+Some OpenKIM models also support writing a new parameter file to a specified location, which can then be used to compile a new OpenKIM model directly. The directory can be specified with the "kim_model_output_directory" and the model name with "kim_model_output_name". If a model does support this feature can be checked with the [[utilities::kim_read_model_props]] utiliy.
+Here is a short example of the additional OpenKIM parameters in the parameter file:
+<code>
+kim_model_name              ex_model_Ar_P_LJ
+kim_model_params            use_default
+kim_model_output_directory  kim_output
+kim_model_output_name       ex_model_Ar_P_LJ_potfit
+</code>