# Initial Concentrations¶

There are three options available for the input of the initial concentrations in the simulation domain. The first one is to set explicitly the concentration for each phase by use of the keyword input. The second option is to specify only the initial concentration of one phase and to calculate the quasi-equilibrium concentrations for all other phases using the equilibrium keyword. The third one allows reading the initial concentration field from a file, similarly to what is done for the initial grain structure, (keyword from_file).

If input is used, the initial concentrations of each constituent in each phase have to be specified, even for phases which might not be present initially. In this case, these values are of less importance and used only under special circumstances in connection with the start_value_1/2 option as initial values for quasi-equilibrium iteration. Use this option, if the initial structure shall be out of equilibrium, or if initial microstructures are read from a restart (.rest) file (see section Initial Microstructure).

If equilibrium is chosen, the concentrations only have to be set for one reference phase, the index of which can be specified as optional parameter in the same line (default is phase 0). Note that, strictly speaking, this condition is a quasi-equilibrium, i.e. there still might be a driving force (parallel tangent construction in case of TQ coupling).

The keyword from_file allows reading initial concentration fields from an ASCII file for each element. In the same line with the from_file keyword, a phase number should be given (default is phase 0). In case of TQ coupling, an estimated composition must be specified for this phase, serving for initialisation of the equilibria at the beginning.

Note: This concentration value has no influence on the initial concentration distribution!

Afterwards, like in the case of reading initial grain structures from file (see section Initial Microstructure), a character must be given which specifies the type of data treatment (n: no action, 1: 1D data, f: mirror top to bottom, t: transpose) as well as the dimensions of the input file have to be given. In case that the geometry of the input file does not correspond to the size of the simulation domain, the data are automatically interpolated.

Note: In case of reading in experimental concentration data, numerical problems may occur with TQ-coupling if the data are noisy or not fully consistent with the initial grain structure!

###### Example 1¶

Driving File
...
# Initial concentrations
# ================
# How shall initial concentrations be set?
# Options:  input  equilibrium  from_file     [phase number]
from_file 1
# Concentration of component 1 (C) in phase 1 (FCC_A1)? [at%] (for initialisation of TQ)
2.00
# File for initialisation of concentration profile of component 1?
Example_conc1.txt
# Treatment of data?
#(n:none, 1:1D, f:flip (bottom<->top), or t:transpose)?
n
# AnzX for initial concentration field of component 1 ?
500
# AnzZ for initial concentration field of component 1 ?
400
# Concentration of component 2 (CR) in phase 1 (FCC_A1)? [at%] (for initialisation of TQ)
0.500
# File for initialisation of concentration profile of component 2?
Example_conc2.txt
# Treatment of data?
#(n:none, 1:1D, f:flip (bottom<->top), or t:transpose)?
n
# AnzX for initial concentration field of component 2 ?
500
# AnzZ for initial concentration field of component 2 ?
400
...


The final input of this section is the temperature for initialisation of the phase interactions between phases present at the beginning of the simulation, i.e. this temperature value is only used for the thermodynamic initialization of those interfaces that already exist in the initial structure.

The result of this initialization process can be seen in the monitoring output (.log-file). Typically, the temperature for initialization is chosen to be identical to the initial temperature at the bottom (see Process Conditions - Temperature). In case of trouble with thermodynamic initialization, the user may try slightly different values.

###### Example 2¶

Initial concentration and temperature for initial equilibrium

# Initial Concentrations
# ======================
# How shall initial concentrations be set?
# Options:  input  equilibrium  from_file     [phase number]
equilibrium
# Initial concentration of component 1 (C) in phase 0 (LIQUID) ? [wt%]
3.6600
# Initial concentration of component 2 (SI) in phase 0 (LIQUID) ? [wt%]
1.9700
# Temperature at which the initial equilibrium
# will be calculated? [K]
1436.0