Initial_Condition
(string, required, no default):
Controls initial momentum distribution of particles.
"peaked momenta"
- All particles have momentum \(p = 3 \cdot T\), where T is the temperature. Directions of momenta are uniformly distributed. "thermal momenta"
- Momenta are sampled from a Maxwell-Boltzmann distribution.Length
(double, required):
Length of the cube's edge, in fm.
Temperature
(double, required):
Temperature in the box, in GeV.
Start_Time
(double, required):
Starting time of the simulation. All particles in the box are initialized with \(x^0\) = Start_Time.
Init_Multiplicities
(int, required):
Map of PDG number and quantity of this PDG number. Controls how many particles of each sort will be initialized.
Use_Thermal_Multiplicities
(bool, optional, default = false):
If this option is set to true then Init_Multiplicities are ignored and the box is initialized with all particle species of the particle table that belong to the hadron gas equation of state, see HadronGasEos::is_eos_particle(). The multiplicities are sampled from Poisson distributions \( Poi(n_i V) \), where \( n_i \) are the grand-canonical thermal densities of the corresponding species and \( V \) is the box volume. This option simulates the grand-canonical ensemble, where the number of particles is not fixed from event to event.
Baryon_Chemical_Potential
(double, optional, default = 0.0):
Baryon chemical potential \( \mu_B \) used in case if Use_Thermal_Multiplicities is true to compute thermal densities \( n_i \).
Strange_Chemical_Potential
(double, optional, default = 0.0):
Strangeness chemical potential \( \mu_S \) used in case if Use_Thermal_Multiplicities is true to compute thermal densities \( n_i \).
The following example configures an infinite matter simulation in a Box with 10 fm cube length at a temperature of 200 MeV. The particles are initialized with thermal momenta at a start time of 10 fm. The particle numbers at initialization are 100 \( \pi^+ \), 100 \( \pi^0 \), 100 \( \pi^- \), 50 protons and 50 neutrons.
Modi: Box: Length: 10.0 Temperature: 0.2 Initial_Condition: "thermal momenta" Start_Time: 10.0 Init_Multiplicities: 211: 100 111: 100 -211: 100 2212: 50 2112: 50
On the contrary, it is also possible to initialize a thermal box based on thermal multiplicities. This is done via
Modi: Box: Length: 10.0 Temperature: 0.2 Use_Thermal_Multiplicities: True Baryon_Chemical_Potential: 0.0 Strange_Chemical_Potential: 0.0
./smash -i INPUT_DIR/box/config.yaml -p INPUT_DIR/box/particles.txt -d INPUT_DIR/box/decaymodes.txt