Calculation of dimers

Reproducing accurate dimer distances is an important difficult benchmark for a potential. If a potential works accurately for dimers and bulk calculations, one can be quite confident that the potential possesses excellent transferability. For the simulation of the dimers, one can use the $\Gamma$ point and displace the second atom along the diagonal direction. Generally bonding length and vibrational frequency have to be compared with accurate reference data. It is recommended to perform these calculations using the constant velocity molecular dynamic mode (i.e. IBRION=2, SMASS=-2). This mode speeds up the calculation because the wave functions are extrapolated and predicted using information from previous steps. The INCAR file must contain additional lines to perform the constant velocity MD:

#ionic relaxation
NSW = 10     #number of steps for IOM
SMASS = -2   #constant velocity MD
POTIM = 1    #time-step for ionic-motion

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