Finding the Values

[SOMASUNDARAM P]

Hi vampire users

I'm new to vampire. How can I determine the appropriate values for total and equilibration time steps when calculating Tc and simulating the Hysteresis loop? 

[gabo...@gmail.com]

Sometimes the values are given in a publication when you are trying to reproduce their results.  When not given in a publication, convergence testing can used for the total and equilibration time steps.

Below is a demonstration of a Curie temperature convergence test for equilibration-time-steps using the Ni workshop files.  The set of equilibration-time-steps were chosen to be 10, 100, 1000, and 10000.  As explained on the VAMPIRE Curie temperature simulation tutorial page at [1], we could have just started with "sim:equilibration-time-steps=10000" as that often times is sufficient to have convergence for that parameter for most systems.  However, doing the calculations with equilibration-time-steps of 10, 100, and 1000 should hopefully illustrate to you the Curie temperature curve changing towards convergence from equilibration-time-steps 10 to 10000:

username@computername:~$ mkdir Ni
username@computername:~$ cd Ni
username@computername:~/Ni$ wget https://raw.githubusercontent.com/richard-evans/vampire-workshop/refs/heads/master/input-files/1_intro/1a_Ni/input
...
username@computername:~/Ni$ wget https://raw.githubusercontent.com/richard-evans/vampire-workshop/refs/heads/master/input-files/1_intro/1a_Ni/Ni.mat
...
username@computername:~/Ni$ ls -l
total 16
-rwxrwxr-x 1 username username  578 Dec 14 18:54 convergence-test.sh
-rw-rw-r-- 1 username username 1584 Dec 14 18:53 input
-rw-rw-r-- 1 username username  792 Dec 14 12:50 Ni.mat
-rw-rw-r-- 1 username username  178 Dec 14 18:55 plotTc
username@computername:~/Ni$ chmod +x convergence-test.sh
username@computername:~/Ni$ ./convergence-test.sh
                                                _          
                                               (_)        
                    __   ____ _ _ __ ___  _ __  _ _ __ ___
                    \ \ / / _` | '_ ` _ \| '_ \| | '__/ _ \
                     \ V / (_| | | | | | | |_) | | | |  __/
                      \_/ \__,_|_| |_| |_| .__/|_|_|  \___|
                                         | |              
                                         |_|              

                      Version 7.0.0 Dec 27 2023 21:29:33

             Git commit: fd9de813cab95bc2b2837122bd03f0238a5d2d76

  Licensed under the GNU Public License(v2). See licence file for details.

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...
Simulation ended gracefully.
username@computername:~/Ni$ gnuplot --persist plotTc

From Table I in the paper at [2], the Curie temperature (Tc) of Nickel should be about 635 K.  For "sim:equilibration-time-steps=10" in the plot, you should see that Tc point occurs above 700 K.  Also, you should see in the plot the move towards convergence of the curves as it goes from  "sim:equilibration-time-steps=10" to the values of 100, 1000, and 10000 with the Tc point being between 600 and 700 K.

[1] https://vampire.york.ac.uk/tutorials/simulation/curie-temperature/

[2] https://arxiv.org/abs/1409.7397v2

Best Regards,

Gavin

VAMPIRE user