questions about emc2

Alloy Theoretic Automated Toolkit (ATAT)
1

Dear Prof. Axel van de Walle and ATAT users,

I’m trying to compute the transition temperature from order to disorder in the canonical ensemble. Here are some questions about using emc2:
(1) My studied system is phase seperation at T=0K. How to correctly use emc2 to simulate the transition tempeature at a certain composion (AxB1-x, x=0.5) in the cannonical ensemble? What I used is,
emc2 -gs=-1 -T0=300 -T1=900 -dT=100 -k=8.617e-5 -cm -x=0 -eq=10000 -n=8000 -er=50 -o=mc10.out

(2) For the output file using the above command, I get a 26 columns output file insted of 18 columns suggested by "emc2 -h". What does each column mean?

(3) "emc2 -h" shows that the sixth column means the variance of the energy(proportional to heat capacity), E2. Could you please tell me what’s the relationship between E2 and heat capacity in detail? And where can I find the references of difference between E2, E-mux, E_lte-mux_lte, E_mf-mux_mf and E_hte-mux_hte?

Thank you very much !
Shuping

2

  1. If the system is phase separating at low T, which order-disorder transition are you trying to get?

  2. emc2 -h clearly indicates that columns 18- (i.e. column 18 and subsquent ones) output the correlations.

  3. See equation for heat capacity at https://en.wikipedia.org/wiki/Partition_function_(statistical_mechanics)
    Also: lte=Low Temperature Expansion, hte=High Temperature Expansion, mf=Mean Field. See https://arxiv.org/abs/cond-mat/0201473

3

The meaning of the first 4 columns are the concentration listed in the same order as in atoms.out

Can you attach your lat.in? (not just the atomic position lines)
I suspect there are some hidden characters in it that confuse the code.

4

Dear Prof. van de Walle,
Thanks for your kindly reply. For your first question `If the system is phase separating at low T, which order-disorder transition are you trying to get ?', I’m trying to get the transition from the phase separation to the solid state solution. Besides, I have several other related questions:

  1. For a binary A_xB_(1-x) cluster expansion system, I want to simulate the MC structures at certain temperature and certain concentration (eg. x=0.6). Strangely, emc2 only outputs the structures at the concentration of x=0.53. How can I deal with it? The commend I used is,
    emc2 -gs=-1 -mu0=0 -mu1=1 -dmu=0.04 -T0=900 -x=0.2 -k=8.617e-5 -cm -eq=10000 -n=8000 -er=50 -oss=60.out -o=mc10.out

  2. I am trying to use mmaps to consider a system that an atom can randomly occupy two sites. In the lat.in file,
    0.5 1.0 1.0 C, Vac
    1.0 0.5 1.0 Vac, C
    The fit.out file (see below) is successfully generated after running mmaps and cluster expanding 42 structures. However, I don’t understand the meaning of the first 4-column in fit.out. It seems that they are the concentrations, but not fully clearly. What does each column mean and why the first two columns are all 0.25?

0.250000 0.250000 0.250000 0.250000 -0.758833 -0.599995 -0.158838 1.000000 0
0.250000 0.250000 0.250000 0.250000 0.533904 0.221711 0.312193 1.000000 1
0.250000 0.250000 0.000000 0.500000 0.000000 -0.247906 0.247906 1.000000 2
0.250000 0.250000 0.500000 0.000000 -0.000000 0.014182 -0.014182 1.000000 3
0.250000 0.250000 0.125000 0.375000 -0.382097 -0.408019 0.025922 1.000000 4
0.250000 0.250000 0.375000 0.125000 -0.358152 -0.424519 0.066368 1.000000 5
0.250000 0.250000 0.250000 0.250000 -0.319973 -0.250614 -0.069360 1.000000 6
0.250000 0.250000 0.250000 0.250000 -0.219417 -0.286754 0.067337 1.000000 7
0.250000 0.250000 0.125000 0.375000 -0.322709 -0.144711 -0.177998 1.000000 8
0.250000 0.250000 0.375000 0.125000 0.195941 0.133878 0.062063 1.000000 9
0.250000 0.250000 0.125000 0.375000 -0.308661 -0.402709 0.094047 1.000000 10
0.250000 0.250000 0.375000 0.125000 -0.387207 -0.468391 0.081184 1.000000 11
0.250000 0.250000 0.250000 0.250000 -0.228552 -0.307245 0.078693 1.000000 12
0.250000 0.250000 0.125000 0.375000 -0.018895 -0.188582 0.169687 1.000000 13
0.250000 0.250000 0.375000 0.125000 0.191681 0.139188 0.052493 1.000000 14
0.250000 0.250000 0.166667 0.333333 -0.496253 -0.472011 -0.024242 1.000000 15
…

Thank you very much!
Shuping

5

Dear Prof. van de Walle,

Thanks for your kindly reply. I’ve solved these problems.

Best wishes!