<div dir="ltr">Dear Matt, thanks for the quick reply. I was thinking along similar lines, since I was wondering how the optimiser would know which direction to follow (for other quantum chemical codes you would have to provide force constants in one way or other). Now, having not used this keyword in CP2K before, could you be a bit more specific about the format? According to the manual, one would explicitly specify the dimer vector in this input section, i.e. ideally I would use the imaginary mode for this.I simply copy this from the _frequenxies.mol output file (the one I have specified to read with molden). Hence the section would look like this: &MOTION &GEO_OPT TYPE TRANSITION_STATE &TRANSITION_STATE METHOD DIMER &DIMER &ROT_OPT OPTIMIZER CG &END ROT_OPT &DIMER_VECTOR -0.000030 -0.000001 -0.000005 0.000019 0.000008 0.000023 -0.000008 -0.000017 -0.000007 <remaining lines> &END DIMER_VECTOR &END DIMER &END TRANSITION_STATE OPTIMIZER CG MAX_FORCE 8.0E-4 MAX_ITER 500 &END GEO_OPT &PRINT &TRAJECTORY &EACH GEO_OPT 1 &END EACH &END TRAJECTORY &END &END MOTION Tobias </div>