digraph cp2k { start [shape=ellipse, label="force_env_calc_energy_force()"]; method [shape=diamond, label="METHOD?", URL="http://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL.html#desc_METHOD"]; start -> method; node [shape=box]; EIP [tooltip="Empirical Interatomic Potential"]; FIST [tooltip="Classical Force Fields"]; MIXED [tooltip="Combine two force-environmens"]; QMMM [tooltip="Hybrid quantum classical"]; QUICKSTEP [tooltip="Electronic structure methods (DFT, ...)", URL="http://cp2k.org/code:qs_forces"]; method -> EIP; method -> FIST; method -> MIXED; method -> QMMM; method -> QUICKSTEP; return [shape=ellipse, label="RETURN"]; EIP -> return; FIST -> return; MIXED -> return; QMMM -> return; QUICKSTEP -> return; }