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Global Control

The general simulation parameters can be defined by the global block. This operator allows to define all control parameters such as the time step, the log/dump/restart frequencies, the log type, and any additional parameter that can be taken as an input by operators called during the simulation. 

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simulation:
  name: MySimulation
  body:
    - print_logo_banner                                  
    - hw_device_init                                     
    - make_empty_grid                                     
    - grid_flavor                                         
    - global                                             
    - [...]
    - simulation_epilog
    - hw_device_finalize

Below is the default definition of the global block as defined in data/config/config_globals.msp (included by default via main-config.msp):

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######################################################################################################
######################################### Default global block  ######################################
######################################################################################################

global:
  max_iteration: 1000                            # number of timesteps
  start_iteration: 0                             # number of timesteps  
  rcut_inc: 1.0 ang                              # skin distance for neighbor list 
  timestep: 0                                    # starting timestep
  physical_time: 0.                              # starting physical time
  dt: 1.0e-3 ps                                  # timestep
  log_mode: mechanical                           # set to chemistry or default

  simulation_restart_frequency: 1000             # restart frequency
  simulation_snapshot_frequency: 1000            # snapshot frequency  
  simulation_analysis_frequency: 1000            # analysis frequency
  simulation_thermostate_file_frequency: 10      # thermostate to file frequency
  thermostate_file: "thermodynamic_state.csv"    # default name of .csv thermostate file
  simulation_thermostate_screen_frequency: 10    # thermostate to screen frequency

  simulation_load_balance_frequency: 100         # load balancing frequency
  enable_load_balance: true                      # enable load balancing
  trigger_cost_model_fitting: false              # for load balancing
  cost_model_coefs: [ 0.0 , 0.0 , 1.0 , 0.0 ]    # for load balancing (RCB)
  enable_grid_compact: true                      # Enable array shrinking of particle arrays
  init_temperature: -1.0
  scale_temperature: -1.0
  md_loop_continue: true                         # needed for the computation loop to start
  trigger_thermo_state: true                     # needed to get the initial thermo state (updated at each iteration, see config_thermostate.msp)
  thermo_state_every_step: false                 # force operators compute energies and virial at every step, not only when used

######################################################################################################
######################################################################################################
Parameters' description
Parameter Description Type Default
max_iteration Ending time-step (maximum number of iterations) int 1000
start_iteration Starting iteration count int 0
rcut_inc Extra distance beyond cutoff (neighbor list skin) float 1.0 ang
timestep Starting time-step value int 0
physical_time Starting physical time float 0.
dt Time-step float 1.0e-3 ps
log_mode Columns of the thermodynamic state (preset name or ;-separated keyword list, see Output) string mechanical
simulation_restart_frequency Restart file write frequency int 1000
simulation_snapshot_frequency Snapshot file write frequency int 1000
simulation_analysis_frequency On-the-fly analysis frequency int 1000
simulation_thermostate_file_frequency Thermodynamic state file write frequency int 10
thermostate_file Name of the thermodynamic state .csv file string "thermodynamic_state.csv"
log_format Optional ;-separated printf formats for the thermodynamic state columns (not set by default, see Output) string —
simulation_thermostate_screen_frequency Thermodynamic state screen-print frequency int 10
simulation_load_balance_frequency Load balancing frequency int 100
enable_load_balance Enables load balancing bool true
trigger_cost_model_fitting Triggers automatic load-balancing cost model fitting bool false
cost_model_coefs Load-balancing cost model coefficients (RCB) list [ 0.0 , 0.0 , 1.0 , 0.0 ]
enable_grid_compact Enables grid memory compaction bool true
init_temperature Initial temperature (disabled if negative) float -1.0
scale_temperature Temperature scaling factor (disabled if negative) float -1.0
md_loop_continue Needed for the simulation loop to start bool true
trigger_thermo_state Force operators compute energies and virial (set at each iteration, see below) bool true
thermo_state_every_step Compute energies and virial at every step, not only when used bool false

Energies and virial are computed only when used

Force operators compute per-atom energies and the virial only on the steps where they are used: when the thermodynamic state is printed or written, or when a restart, a snapshot or an analysis is due. On the other steps they compute forces only, which is faster. Schemes that need energies or the virial at every step (Nosé-Hoover NPT, Parrinello-Rahman, FIRE and conjugate gradient minimizations) request them automatically. If a custom operator reads per-atom energies or the virial at every step, set thermo_state_every_step: true.

In practice, the user doesn't need to think about some of these variables as they only serve as input for the simulation initialization. Here's a minimal global block you can use to start your simulation with.

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global:
  max_iteration: 1000                            # number of timesteps
  rcut_inc: 1.0 ang                              # skin distance for neighbor list 
  dt: 1.0e-3 ps                                  # timestep
  simulation_restart_frequency: 1000             # restart frequency
  simulation_snapshot_frequency: 1000            # snapshot frequency  
  simulation_analysis_frequency: 0               # analysis frequency
  simulation_thermostate_file_frequency: 10      # thermostate to file frequency
  thermostate_file: "thermodynamic_state.csv"    # default name of .csv thermostate file
  simulation_thermostate_screen_frequency: 10    # thermostate to screen frequency