How can i simulate 10^12 particles simultaneously?

Particles, Track, Event, Run and Biasing
2

You can’t, not in a single run. The number of events is stored in a signed integer (G4int), with a maximum value of 2,147,483,647. To generate that many events, you should do five runs of maximum size in your job:

/run/beamOn 2000000000
/run/beamOn 2000000000
/run/beamOn 2000000000
/run/beamOn 2000000000
/run/beamOn 2000000000

Set up your analysis code so that it either accumulates across all the runs of a job, or includes the run number (which increments with each beamOn) in the output filename.

If you want to run your jobs in parallel, you will need to write your own code to initialize the random number seed uniquely for each job (in my experiment, we wrote a utility class to generate seeds from UUIDs; you could use the timestamp, job ID, or something).

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