MultiComponent Easy Monte Carlo Code (emc2) by Axel van de Walle Command line parameters: -er : enclosed radius. The Monte Carlo cell will the smallest possible supercell of unit cell of the initial configuration such that a sphere of that radius fits inside it. This allows you to specify the system size in a structure-independent fashion. -cf : Control file specifying the ranges of temperature and chemical potentials scanned (default: control.in). See file format below. -eq : number of equilibration passes. (Equilibration is performed at the beginning of each step of the outer loop.) -n : number of Monte Carlo passes performed to evaluate thermodynamic quanties at each step of the inner loop. -tp : instead of specifying -eq and -n, you can ask the code to equilibrate and run for a time such that the average energy is accurate within the target precision specifified by -tp=. -aq : Alternative quantity that must meet the tolerance specified by -tp. 0: energy (default), 1: long-range order, 2-: concentations, correlations -gs : Gives the index of the ground state to use as an initial spin configuration (starting at 0). The ground states are listed in gs_str.out. If the index is -1, the disordered state with equiatomic composition is used. (If -gs=-1, the LTE and MF approximations are not calculated. If you want the LTE and MF ouputs, use one of the 'pure' end members as a starting point.) -tstat : Critical value of the test for discontinuity. The code is able to catch phase transformations (most of the time) when going from an ordered phase to another or to the disordered state. This involves a statistical test which a user-specified confidence level. The default, 3, corresponds to a 0.4% chance of finding a transition where there is none. (Refer to a standard normal table.) -tstat=0 turns off this option. Suggestion: if a phase transition is undetected, first try to reduce temperature or chem. pot. steps or increase n or decrease tp before toying around with this parameter. Also: beware of hysteresis. -sigdig : Number of significant digits printed. Default is 6. -o: Name of the output file (default: mc.out). -k : Sets boltzman's constant (default k=1). This only affects how temperatures are converted in energies. -k=8.617e-5 lets you enter temperatures in kelvins when energies are in eV. (You can also select this value by using the -keV option.) -mft : Mean field threshold. If the grand canonical potential obtained via the mean field approximation and the low temperature expansion are less than this threshold, Monte Carlo simulation are skipped and mean field values are used instead. (They replace the MC values in the output file. The column labelled use_mf is equal to 1 when this substitution is made. Note: When use_mf=1, the correlations in the output file are incorrectly set to their values in an ideal fully ordered structure. All other columns are reliable. -mftq: Quantity that must meet the tolerance specified by -mft. 0: phi (default) , 1: energy , 2: long-range order, 3-: concentrations Tricks: To read parameters from a file, use: memc2 `cat inputfile` where inputfile contains the commands line options. To selectively display a few of the output quantities, use: memc2 [options] | cut -f n1,n2,n3,... where n1,n2,n3,... are the column number desired (see below). -> Input files: control.in : range of temperature and chemical potentials to scan. The first line of this file specifies the initial conditions and has the format: temperature chemical_potentials_1 ... chemical_potentials_n where the chemical potentials are for each specie. Each subsequent line of this file indicates one of the axes along which to scan and has the format: temperature chemical_potentials_1 ... chemical_potentials_n number_of_steps where number_of_steps is the the number of steps made between the initial conditions and the final conditions given on the line. Example: to scan the region in (T,mu1,mu2,mu3)-space defined by 100 <= T < 200 and 0 <= mu1 < 1.0 and 0 <= mu2 < 0.5 and mu3 == 0.0 with a 10x5x5 grid the control.in file should be 100 0.0 0.0 0.0 200 0.0 0.0 0.0 10 100 0.0 0.5 0.0 5 100 1.0 0.0 0.0 5 Note: Temperatures are given in units of energy unless the -k or -eV options are set. By default, the finals conditions are excluded from the scan (in the example above the chemical potentials scanned in the last line are 0.0 0.2 0.4 0.6 0.8) This behavior can be changed with the -il option, to give: 0.0 0.25 0.5 0.75 1.0) Alternatively, the -hf option gives: 0.1 0.3 0.5 0.7 0.9 . NOTE: The mmaps code generates a file called chempot.out which contains special values of the chemical potential that stabilize various types of equilibria. These values are useful guidelines to select relevant regions in mu-space to scan. -> Other input files: lat.in : description of the lattice. clusters.out : describes the clusters. eci.out : provides the ECI. gs_str.out : a list of ground states, in no particular order. These 4 files can be created by maps. See maps documentation (maps -h) for a description of the formats. -> Optional input files: teci.out : if present, provides temperature-dependent eci (overrides eci.out) (Note that, even when the teci.out file is used, column 6 of the output file reflects only the configurational contribution to the heat capacity.) The format this file is: [maximum temperature: Tm] [number of temperatures where eci are provided: nT] [ECIs for temperature 0] [ECIs for temperature Tm/(nT-1)] [ECIs for temperature 2*Tm/(nT-1)] ... [ECIs for temperature Tm] Note that these numbers can be seperated by blanks or newlines, as desired. conccons.in : Specifies linear constraints on the composition that spin flips must obey. (The code will generate multi-spin flips if necessary.) Here is an example of such file: 1.0*Al -1.0*Li +0.1*Co = 0.5 Please use rational numbers only - infinite loop will result otherwise. Composition is determined by the user-supplied initial configuration (via the -g or -is options). This input file replaces and generalizes the -cm option in emc2. -> Format of the output file The file mcheader.out gives the content of column of the output file. The following abreviations are used: T: temperature mu(A): chemical potentials of specie A x(A): concentration of specie A E: energy (per active site) Egc: grand canonical energy (per active site) , i.e., E - sum_i mu(i)*x(i) lro: long Range Order parameter of the initial ordered phase (=0 if initial phase is disordered) F: Helmholtz free energy (per active site) phi: grand canonical potential: F - sum_i mu(i)*x(i) use_mf: flag that is 1 if mf values have been used instead of mc values corr_n_d: the average correlations associated with each cluster n is the number of points in the cluster d is the diameter of the cluster Suffixes: _lte: obtained with low temperature expansion _mf: obtained with mean field approximation _mc: obtained with Monte Carlo simulations NOTE: to obtain 'canonical' rather than grand canonical quantities (adding mu*x), to all (free) energies use the -g2c option. NOTE: an 'active site' is one that can host more than one possible atom type. Energy and free energy are reported per 'active site' not per total sites.