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Short helpfile for action OPES_METAD
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The following arguments are compulsory: 

                   TEMP - ( default=-1 ) temperature. If not set, it is taken from MD 
                          engine, but not all MD codes provide it 
                   PACE - the frequency for kernel deposition 
                  SIGMA - ( default=ADAPTIVE ) the initial widths of the kernels. If 
                          not set, adaptive sigma will be used with the given 
                          ADAPTIVE_SIGMA_STRIDE 
                BARRIER - the free energy barrier to be overcome. It is used to set 
                          BIASFACTOR, EPSILON, and KERNEL_CUTOFF to reasonable values 
  COMPRESSION_THRESHOLD - ( default=1 ) merge kernels if closer than this threshold, 
                          in units of sigma 
                   FILE - ( default=KERNELS ) a file in which the list of all 
                          deposited kernels is stored 

In addition you may use the following options: 

  NUMERICAL_DERIVATIVES - ( default=off ) calculate the derivatives for these 
                          quantities numerically 
                  NLIST - ( default=off ) use neighbor list for kernels summation, 
                          faster but experimental 
       NLIST_PACE_RESET - ( default=off ) force the reset of the neighbor list at 
                          each PACE. Can be useful with WALKERS_MPI 
            FIXED_SIGMA - ( default=off ) do not decrease sigma as the simulation 
                          proceeds. Can be added in a RESTART, to keep in check the number of 
                          compressed kernels 
    RECURSIVE_MERGE_OFF - ( default=off ) do not recursively attempt kernel merging 
                          when a new one is added 
                 NO_ZED - ( default=off ) do not normalize over the explored CV 
                          space, \f$Z_n=1\f$ 
           STORE_STATES - ( default=off ) append to STATE_WFILE instead of ovewriting 
                          it each time 
              CALC_WORK - ( default=off ) calculate the total accumulated work done 
                          by the bias since last restart 
            WALKERS_MPI - ( default=off ) switch on MPI version of multiple walkers 
                 SERIAL - ( default=off ) perform calculations in serial 
                    ARG - the input for this action is the scalar output from one or 
                          more other actions. The particular scalars that you will use are 
                          referenced using the label of the action. If the label appears on its 
                          own then it is assumed that the Action calculates a single 
                          scalar value. The value of this scalar is thus used as the input 
                          to this new action. If * or *.* appears the scalars calculated 
                          by all the proceeding actions in the input file are taken. 
                          Some actions have multi-component outputs and each component of 
                          the output has a specific label. For example a \ref DISTANCE 
                          action labelled dist may have three components x, y and z. To take 
                          just the x component you should use dist.x, if you wish to take 
                          all three components then use dist.*.More information on the 
                          referencing of Actions can be found in the section of the manual on the 
                          PLUMED \ref Syntax. Scalar values can also be referenced using 
                          POSIX regular expressions as detailed in the section on \ref 
                          Regex. To use this feature you you must compile PLUMED with the 
                          appropriate flag. You can use multiple instances of this keyword i.e. 
                          ARG1, ARG2, ARG3... 
  ADAPTIVE_SIGMA_STRIDE - number of steps for measuring adaptive sigma. Default is 
                          10xPACE 
              SIGMA_MIN - never reduce SIGMA below this value 
             BIASFACTOR - the \f$\gamma\f$ bias factor used for the well-tempered 
                          target \f$p(\mathbfs)\f$. 
                EPSILON - the value of the regularization constant for the 
                          probability 
          KERNEL_CUTOFF - truncate kernels at this distance, in units of sigma 
       NLIST_PARAMETERS - ( default=3.0,0.5 ) the two cutoff parameters for the 
                          kernels neighbor list 
                    FMT - specify format for KERNELS file 
            STATE_RFILE - read from this file the compressed kernels and all the info 
                          needed to RESTART the simulation 
            STATE_WFILE - write to this file the compressed kernels and all the info 
                          needed to RESTART the simulation 
          STATE_WSTRIDE - number of MD steps between writing the STATE_WFILE. Default 
                          is only on CPT events (but not all MD codes set them) 
        EXCLUDED_REGION - kernels are not deposited when the action provided here has 
                          a nonzero value, see example above 
             EXTRA_BIAS - consider also these other bias potentials for the internal 
                          reweighting. This can be used e.g. for sampling a custom target 
                          distribution (see example above) 
                RESTART - allows per-action setting of restart (YES/NO/AUTO) 
            UPDATE_FROM - Only update this action from this time 
           UPDATE_UNTIL - Only update this action until this time 


