modify environment
   archive which         # 1
      seed value            # 2
      time ps               # 3
   #
      velocities how        # 4
      temperature T         # 5
      start_temperature Ts  # 6
      final_temperature Tf  # 7
   #
      lockset set           # 8
   end

Modify the environment of the molecular system: (1) set the type of records to be saved in future archive commands or in the periodic archiving of the simulation methods; the preset value of which is coordinates meaning only coordinates will be saved, other acceptable values are velocities to save only velocities and both to save both coordinates and velocities. (2) Seed the random number generator with value; the preset value is 1. (3) Set the clock to ps picoseconds; at the start of the run ps is set to the value read from the archive file, otherwise the time is set to zero; the next molecular dynamics run will start from this time value; the time does not affect the simulation, it is merely a book-keeping device.

(4) Generate a new set of velocities at the target starting temperature if how equals new otherwise scale the current velocities to the target starting temperature if how equals scale. Scaling does not work if the current velocities are undefined or all-zero. (5) Set the target starting and final temperatures to the value T, the preset value of T is 300.0 K. (6) Set the target starting temperature to the value Ts, the preset value is 300.0 K (7) Set the target final temperature to the value Tf, the preset value is 300.0 K. The target temperatures are simply that. At the next run of the molecular dynamics or monte carlo methods, the temperature will be varied linearly from the starting temperature to the final temperature. The variation in the temperature is achieved in molecular dynamics by periodic resetting of the velocities (see modify dynamics) while temperature is controlled as a direct variable in monte carlo.

(8) Choose a lock set. Each set is a group of atoms defined in the descriptor file. During a simulation, these atom groups can be chosen to be locked at their current positions. Locking is effective only in certain energy minimization methods and the monte carlo method. In particular, the molecular dynamic methods ignore atom locking. The preset value of set is 0 meaning no lock set is chosen.