====== Example: Kawamura potential ====== ---- The Kawamura potential is commonly used for UO$_2$, see [[http://dx.doi.org/10.1016/S0925-8388(00)00806-9|this article]]. The notation for this potential is rather unusual. There is only one function for a binary system, where one usually has three potentials. //potfit// essentially needs three functions for "ntypes = 2". However, there is an elegant solution to this problem, using global parameters. To define a proper "kawamura" potential for UO$_2$ one can use the following potential file: #F 0 3 #T PAIR #C U O #I 0 0 0 #E global 12 z_U 1.86 1 3 z_O -1.2 -3 -1 f0 4.186 1.0 10.0 a_U 0.54 0.1 2.5 a_O 1.26 0.1 2.5 b_U 0.16 0.1 0.4 b_O 0.16 0.1 0.4 c_U 0 0 50 c_O 20 0 50 D 18 0 50 Beta 1.25 0 5 r0 1.61 1.4 1.8 type kawamura cutoff 7.0 z_U! z_U! f0! a_U! a_U! b_U! b_U! c_U! c_U! type kawamura_mix cutoff 7.0 z_U! z_O! f0! a_U! a_O! b_U! b_O! c_U! c_O! D! Beta! r0! type kawamura cutoff 7.0 z_O! z_O! f0! a_O! a_O! b_O! b_O! c_O! c_O! While this looks rather cumbersome, it will optimize only the 12 global parameters, which are shared among the three interactions in the binary system.