Keywords and Syntax in POP File

One of the commonly used experimental data file formats is POP. The POP format has been widely accepted in CALPHAD community. PanOptimizer accepts most of the keywords in POP forma and adds a few special keywords. The keywords and syntax accepted in PanOptimizer are summarized below in Table 1. PanOpimizer is case insensitive to the following keywords.

**Table 1:** Keywords and Syntax in POP File
Command	Syntax
Create_New_Equilibrium	Create_New_Equilibrium [integer1], integer2 This command defines specific phase equilibrium. Each experimental equilibrium must start with the CREATE command. The first integer is a unique identifier, and the second integer is an initialization code, for which 0 means that all components and phases are initially suspended, 1 means that all components are entered but all phases suspended, 2 means all components and phase are initially entered.
ENTER_SYMBOL CONSTANT	ENTER_SYMBOL CONSTANT dT=200 This command can be used to define a constant value which appears in pop files more than once as a symbol.
ENTER_SYMBOL Function	ENTER_SYMBOL FUNCTION SXS=-100+8.314*T This command can be used to define a function which appears in pop files more than once as a symbol.
COMMENT	COMMENT [string] this will be used for legend text when merged with the phase diagram
Change_Status	Change_Status [Phase] [Name] = [Status] [Value] This command defines the status of selected phases. Four statuses are allowed: Fixed, Suspended, Dormant, and Entered. The value is an initial phase amount for Entered phases (PanOptimizer will use this value as a start value for the Entered phase to solve the phase equilibrium). The exact value of phase amount must be provided for Fixed phases.
Set_Condition	Set_Condition [state variable 1 = value] [state variable 2 = value]... This command defines the calculation conditions at which the degree of freedom of the system is zero and the phase equilibrium can be calculated. Examples of conditions are temperature, pressure, and composition, or a constraint function. Uncertainty can be added to each condition.
Set_Reference_State	Set_Reference_State [component] [reference states] This keyword defines the reference state of a component. The field of reference state includes phase name, temperature and pressure in sequence.
Experiment	Experiment[state variable 1 = value : uncertainty] [state variable 2 = value : uncertainty] This keyword specifies the quantity to be fitted by the optimization. The syntax of this command is similar to the command of Set_Condition. It is followed by a state variable or a function name and a value and an uncertainty.
Set_Start_Value	Set_Start_Value [state variable 1 = value]…… This keyword is mainly used if the phase described by complicated compound energy model. It is also used for phases with fixed status. The most frequently used variable is site fraction of sublattice. PanOptimizer can automatically search the site fractions of components and species when the phases are in entered status
Table_Head Table_Values Table_End	Table_Head, Table_Values and Table_End The three keywords define a set of phase equilibria under similar conditions. The keyword Table_Head must be followed by Create_New_Equilibrium.

**Table 2:** Recognized variables used in defining experimental data
Function Name	Syntax
T	Temperature in the system (in K).
P	Pressure in the system (in Pascal).
N	System size (mole number in moles)
X	X(comp): overall molar fraction of a component in a system. X(phase, comp): molar fraction of a component in a phase.
W	W(comp).: overall weight fraction of a component in a system. W(phase, comp): weight fraction of a component in a phase.
Y	Y(phase,constituent # sublattice): The site fraction of the constituent in certain sublattice of the phase. For example: Y(Sigma,Fe#3) is the site fraction Fe in the third sublattice of the Sigma phase.
GM, HM, SM	GM(phase), HM(phase), SM(phase) Gibbs energy, enthalpy and entropy of phase per mole of atoms.
GMR, HMR, SMR	GMR(phase), HMR(phase), SMR(phase) Gibbs energy, enthalpy and entropy of phase per mole of atoms with given reference state.
Cp	Cp(phase): The heat capacity of a phase.
ACR	ACR(comp, phase) Activity of component in a phase with a given reference state.
MU	MU(comp), MU(phase,comp) Chemical potential of component in system or phase.
MUR	MUR(comp), MUR(phase,comp) Chemical potential of component in system or phase with given reference state.
M, LOGM	M(phase, K), LOGM (phase, K) Mobility coefficient or log10 of the mobility coefficient where K = diffusing species.
DT, LOGDT	DT(phase, K), LOGDT(phase, K) Tracer diffusion coefficient or log10 of the tracer diffusion coefficient where K = diffusing species.
DC, LOGDC	DC(phase, K, J, N), LOGDC(phase, K, J, N) Chemical diffusion coefficient or log10 of the chemical diffusion coefficient where J = gradient species and N = reference species. Note: the reference species N must be given for DC calculation.
NPF	NPF(phase): mole phase fraction of the given phase.
DGM	DGM(phase): The driving force of the given phase.
TC	Curie temperature for magnetic ordering
BMAGN	Bohr magneton number for magnetic ordering
VM, DS, MW, VS, ST	VM(phase), DS(phase), MW(phase), VS(Phase), ST(phase) Molar volume, density, molecular weight, viscosity and surface tension of phase.