System

From PIMC++

There are a number of different paramaters used to define the physical system on which the simulation is performing. They include things such as the number of time slices, the time step, information about the species, the box, etc.

They are all included in the section System

Example input:

Section (System)
{
  int NumTimeSlices=80;  
  double tau=0.025;
  Array<double,1> Box(3)=[11.01,  12.713,  11.98];
  Array<bool, 1 > IsPeriodic(3)=[true,true,true];
  Section (Particles)
  {
    Section (Species)
    {
      string Name="He";
      string Type="He";
      double lambda=6.059615;
      string Statistics="BOSON";
      int NumParticles=48;
      int NumDim=3;
      string InitPaths="BCC";
    }

  }

}

At the level of System (i.e. not at a lower level in the hierarchy) the parameters are:

NumTimeSlices: Specifies the number of time slices for the system. The beta of the system is defined as tau*NumTimeSlices

tau: Specifies the time step (in the trotter breakup) for the simulation.

Array<bool,1> IsPeriodic(3): Specifies which dimensions the system is periodic in. Currently an entirely periodic box is well tested and a box with no periodicity should largely work. A box that is periodic in only some dimensions is not well implemented right this second but could be without too much difficulty.

Array<double,1> Box(3): Specifies the size of the box for the system. Must be the number of dimensions of the entire system.

The System section, contains a section Particles that defines parameters associated with the particles.

The Particles section defines a Species section for each species in the simulation.

Each Species' in the simulation is set up in a section Species inside the section Particles which is inside the section System

Example input:

Section (Species)
   {
     string Name="He";
     string Type="He";
     double lambda=6.059615;
     string Statistics="BOSON";
     int NumParticles=48;
     int NumDim=3;
     string InitPaths="BCC";
   }

The paramaters that are required to define a species are:

Paramaters: Type: Specifies the type of the species. This is used to look up its Pair Action and must correspond to the corresponding name inside the PairAction file.

Name: This is a user-supplied name that will be used to reference the species. lambda: Equal to \hbar^2/2m.

Statistics: string variable indicating the statistics of the particle. Choice of "Boson", "Fermion" or "Boltzmannon". Currently using the "Fermion" flag turns on some of the nodal actions. None of the other flags currently do anything. Maybe we should check if the Boson flag is on before allowing permutations to happen.

NumParticles: How many particles of this type are being used in the simulation.

NumDim: The dimensionality of this particle. Lower dimensions then the number of dimensions of the simulation will allow things such as strings and planes as particles but this currently does not work.

InitPaths: string used to specify how to initialize the particles. Choices are:

1. BCC: Sets up the particles in a BCC lattice
2. FIXED: Allows you to specifiy the intial conditions of all the particles. All time slices will start at the same initial condition. Using this paramater requires the use of the paramater
3. Array <double,2> Positions(numParticles,NDIM): Specifies the particle locations.
4. FILE: Allows you to specify a file from which the last configuration in the PathDump of the file will be read. Using this flag requires the user of the paramater
   1. string File="fileName": Specifies the BASE (no .0.h5) of the filename to be read. If cloning is being used it will attempt to read fileName.n.h5 for the n'th clone.