> version contains a minimum at 0. I agree with OB implementation that this is > not at all true but I want to know the origin of the expression you have > used. One important feature that can be obtained in Rappé's formulation is > that after taking the second derivative of the energy respect to the angle, > evaluated at the minumum always gives K_ijk for any coordination. This is not > recovered from the expression in OB (that value for trigonal planar is > 4K_ijk/3).
I like the *concept* of Rappé’s formulation, but in principal, it’s a royal pain because crude geometries with closely-spaced atoms (i.e. highly acute angles) never get corrected. Worse, with the minima at 0.0 degrees, atoms optimize to the same position! The angular expressions are crude attempts by myself to roughly retain the appropriate angular minima. I’m open to other expressions and indeed would really love if anyone wants to work with me on fixing and re-parameterizing UFF. It’s one of the few force fields that works with so many elements and strange metal coordinations. But it doesn’t easily handle metallocenes, has these typos in the original paper, and has minima at 0.0 degrees. One way I considered adjusting the angular formulas was to take into account VdW repulsion at low angles, but never had the time to work out an analytical expression. Thoughts? Suggestions? Critiques? Thanks, -Geoff ------------------------------------------------------------------------------ Sponsored by Intel(R) XDK Develop, test and display web and hybrid apps with a single code base. Download it for free now! http://pubads.g.doubleclick.net/gampad/clk?id=111408631&iu=/4140/ostg.clktrk _______________________________________________ OpenBabel-discuss mailing list OpenBabel-discuss@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openbabel-discuss
