Lower than expected value of Tc of 2D Mxene

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danial asad

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Jul 25, 2022, 1:01:48 AM7/25/22
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Dear Vampire users,

I am trying to calculate Tc of 2D Cr based Mxene (Cr2NO2) which has hexagonal/kagome structure. I see that the previous paper (ACS Nano 2017, 11, 7648−7655) gives a Tc of ~550 K, probably using probably VAMIRE. However, when I use J1 and J2 given in this paper (J1=1.83 meV, J2= 2.87 meV), the value of Tc obtained is an order of magnitude smaller. Moreover, the value of Tc remains almost independent of the value of magnetic moment in mat file

I am a new to VAMPIRE, so it is possible that I doing some mistake while making input files which are given below:
___________________________________________________________________________________

UCF

#unit cell vectors
1    0    0
0    1    0
0    0    1
#Atoms
4    0
0    0.000000000         0.000000000         0.0474244499    0    0       0
1    0.000000000         0.333333499         0.0581745338    0    0    0
2    0.500000000         0.500000000         0.0474244499    0    0    0
3    0.499999625         0.833333521         0.0581745338    0    0    0
#interactions
36    isotropic
0    0    1    0    0    0    2.93e-22
1    0    3    0    -1    0    2.93e-22
2    0    3    -1    -1    0    2.93e-22
3    1    0    0    0    0    2.93e-22
4    1    2    0    0    0    2.93e-22
5    1    2    -1    0    0    2.93e-22
6    2    3    0    0    0    2.93e-22
7    2    1    0    0    0    2.93e-22
8    2    1    1    0    0    2.93e-22
9    3    2    0    0    0    2.93e-22
10    3    0    0    1    0    2.93e-22
11    3    0    1    1    0    2.93e-22
12    0    0    -1    0    0    4.60e-22
13    0    2    -1    0    0     4.60e-22    
14    0    2    0    0    0    4.60e-22
15    0    0    1    0    0    4.60e-22
16    0    2    0    -1    0    4.60e-22    
17    0    2    -1    -1    0    4.60e-22
18    1    1    -1    0    0    4.60e-22
19    1    3    -1    0    0    4.60e-22
20    1    3    0    0    0    4.60e-22
21    1    1    1    0    0    4.60e-22
22    1    3    0    -1    0    4.60e-22
23    1    3    -1    -1    0    4.60e-22
24    2    2    -1    0    0    4.60e-22
25    2    0    0    1    0    4.60e-22
26    2    0    1    1    0    4.60e-22
27    2    2    1    0    0    4.60e-22
28    2    0    1    0    0    4.60e-22
29    2    0    0    0    0    4.60e-22
30    3    3    -1    0    0    4.60e-22
31    3    1    0    1    0    4.60e-22
32    3    1    1    1    0    4.60e-22
33    3    3    1    0    0    4.60e-22
34    3    1    1    0    0    4.60e-22
35    3    1    0    0    0    4.60e-22   

mat

#===================================================
# Sample vampire material file V5
#===================================================

#---------------------------------------------------
# Number of Materials
#---------------------------------------------------
material:num-materials=1
#---------------------------------------------------
# Material 1 Cr Generic
#---------------------------------------------------
material[1]:material-name=Cr
material[1]:atomic-spin-moment=3.5 !muB
material[1]:initial-spin-direction = 1,0,0
material[1]:uniaxial-anisotropy-constant=0.816e-23
material[1]:material-element=Cr

input

#------------------------------------------
# Creation attributes:
#------------------------------------------
create:periodic-boundaries-x
create:periodic-boundaries-y
create:periodic-boundaries-z
#------------------------------------------
# System Dimensions:
#------------------------------------------
dimensions:system-size-x = 20.0 !nm
dimensions:system-size-y = 20.0 !nm
#------------------------------------------
# Material Files:
#------------------------------------------
material:file = mat
material:unit-cell-file= = ucf
#------------------------------------------
# Simulation attributes:
#------------------------------------------
sim:minimum-temperature =0
sim:maximum-temperature = 500
sim:temperature-increment = 25
sim:time-steps-increment = 1
sim:equilibration-time-steps = 1000000
sim:loop-time-steps = 1000000

#------------------------------------------
# Program and integrator details
#------------------------------------------
sim:program = curie-temperature
sim:integrator = monte-carlo
#------------------------------------------
# data output
#------------------------------------------
output:real-time
output:temperature
output:magnetisation
output:magnetisation-length
output:mean-magnetisation-length

screen:temperature
screen:mean-magnetisation-length
______________________________________________________________________________________

I have confirmed that the structure is reproduced correctly by using vdc.

I will thoroughly appreciate if VAMPIRE experts can point out reasons/errors responsible for this discrepancy.

with best regards
Danial

danial asad

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Jul 25, 2022, 1:50:42 AM7/25/22
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With reference to  my  previous post, the first few lines of the UCF file were omitted accidentally. The complete UCF file for Cr2NO2, containing only Cr atoms is given below:

UCF

#unit cell size
2.99 5.17883 200

#unit cell vectors
1 0 0
0 1 0
0 0 1
#Atoms
4 0
0 0.000000000         0.000000000         0.0474244499 0 0       0
1 0.000000000         0.333333499         0.0581745338    0 0 0
2 0.500000000         0.500000000         0.0474244499 0 0 0
3 0.499999625         0.833333521         0.0581745338 0 0 0
#interactions
36 isotropic
0 0 1 0 0 0 5.76e-22
1 0 3 0 -1 0 5.76e-22
2 0 3 -1 -1 0 5.76e-22
3 1 0 0 0 0 5.76e-22
4 1 2 0 0 0 5.76e-22
5 1 2 -1 0 0 5.76e-22
6 2 3 0 0 0 5.76e-22
7 2 1 0 0 0 5.76e-22
8 2 1 1 0 0 5.76e-22
9 3 2 0 0 0 5.76e-22
10 3 0 0 1 0 5.76e-22
11 3 0 1 1 0 5.76e-22
12 0 0 -1 0 0 3.46e-22
13 0 2 -1 0 0 3.46e-22
14 0 2 0 0 0 3.46e-22
15 0 0 1 0 0 3.46e-22
16 0 2 0 -1 0 3.46e-22
17 0 2 -1 -1 0 3.46e-22
18 1 1 -1 0 0 3.46e-22
19 1 3 -1 0 0 3.46e-22
20 1 3 0 0 0 3.46e-22
21 1 1 1 0 0 3.46e-22
22 1 3 0 -1 0 3.46e-22
23 1 3 -1 -1 0 3.46e-22
24 2 2 -1 0 0 3.46e-22
25 2 0 0 1 0 3.46e-22
26 2 0 1 1 0 3.46e-22
27 2 2 1 0 0 3.46e-22
28 2 0 1 0 0 3.46e-22
29 2 0 0 0 0 3.46e-22
30 3 3 -1 0 0 3.46e-22
31 3 1 0 1 0 3.46e-22
32 3 1 1 1 0 3.46e-22
33 3 3 1 0 0 3.46e-22
34 3 1 1 0 0 3.46e-22
35 3 1 0 0 0 3.46e-22

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gabo...@gmail.com

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Jul 25, 2022, 4:36:14 AM7/25/22
to Vampire Users
Refer to "Which papers should I cite if I publish results using vampire?" under the VAMPIRE FAQs at [1].

In the list of references for ACS Nano 2017, 11, 7648−7655 at [2], I'm not seeing a citation to one of the VAMPIRE articles in the FAQs.  That probably means VAMPIRE was not used.  Thus, the authors of that paper might have made their own simulation program for that.  Thus, their result might only be reproducible with the author's custom source code.  I do see that the corresponding author's email address is there at [2] for contacting the authors of that paper as a way for you to possibly request the program they used and get more information on the MC simulation of Tc they did for CrNO2.


Kind Regards,
Gavin
VAMPIRE user

danial asad

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Jul 25, 2022, 4:55:32 AM7/25/22
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Dear Gavin,

While the paper does not cite VAMPIRE, it is cited in the PhD thesis of one of the co-author (Nathan Frey) for the calculation of Tc for the same materials. This is why I think they used VAMPIRE for actual calculations. But even if they are using their own or other available code, I find it rather bizarre that similar J1 and J2 should give such drastically different results for Tc.
Moreover, this problem is not just restricted to this paper but I am also not able to reproduce Tc for other Mxene and 2D magnetic like CrI3.Therefore, I was wondering whether I am making some mistake in the input files which is causing this discrepancy.

anyways, thanks for your response

saqib





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gabo...@gmail.com

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Jul 25, 2022, 6:05:36 AM7/25/22
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I'm not seeing VAMPIRE files (input, .mat, .ucf) in Nathan's PhD thesis [1]. If they did use that, maybe you can contact the advisor Prof. Shenoy [2] to see if you can get them for comparison with yours.  It might also be important to find out what version of VAMPIRE they used.  Many of the older versions of VAMPIRE I haven't used.  So I'm not familiar with whether or not there were any severe bugs throughout the VAMPIRE releases. 

I see that the ACS abstract [3] has Cr2NO2 with Tc = 566 K, whereas Table 3.1 on page 42 in the PhD thesis [1] has Tc = 53 K for Cr2NO2.

Reproducing an article's result can at times be difficult, as sometimes the VAMPIRE version is not given, the software (operating system, compilers, libraries) and hardware used to perform the calculation is not given, not all simulation parameters might be there in the article due to publication page limits, and the history of the steps in which the calculation was run might not be given or available.  Any one or a combination of those such things can potentially cause a simulation result to come out different.

Kind Regards,
Gavin
VAMPIRE user

danial asad

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Jul 25, 2022, 6:21:10 AM7/25/22
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It will still be a great surprise if Tc estimates are changed by an order of magnitude while going from one version to another. All the issues you have mentioned (libraties etc) can't possibly explain this drastic difference.
I hope that VAMPIRE developers can comment on these issue since this difference may arise owing to some missing parameter in one of the input files

best


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gabo...@gmail.com

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Jul 25, 2022, 6:49:31 AM7/25/22
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Likely you are right that it is due to a missing parameter as I haven't noticed anything with your input files based on the available information.  Perhaps, one of the others in the list sees something I don't.

Of note, users did report some similar issues with Tc in the past.

A couple of them are below, but there may have been others.


2.
-----------------------------------------------------------------------------------------------------------------------------------------------------
On 7/30/2020 5:08 AM, Shuo Li wrote:
Hello everyone,
I figure out which part is wrong.   The J interaction of atom-atom I considered is not enough.    If you want to simulate Tc, you should consider isotropic interactions based on your system and its symmetry.

Best,

在 2020年7月24日星期五 UTC+2下午4:33:17，Shuo Li写道：
I consider J1, J2 and J3  for 2d materials,  J is over 50 meV.  So I think I can get a high Curie temperature over room temperature. However, I got 80 K.

https://iopscience.iop.org/article/10.1088/1361-6528/ab70fc   In this paper, they get the J is about 8 meV, and the Curie temperature is 110 K.

 I don't know which parameter is wrong.  Thanks in advance.
---------------------------------------------------------------------------------------------------------------------------------------------------------------

Kind Regards,

Gavin
VAMPIRE user

milton...@gmail.com

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Aug 18, 2022, 8:34:30 AM8/18/22
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Ye there are more people encountering the problem: https://groups.google.com/g/vampire-users/c/dSW2CpF26go
Whenever I try to use exchange values from some ab-initio paper I always get way lower Tc than they do. I don't know what Shuo Li means by "you should consider isotropic interactions based on your system and its symmetry" but I have tried multiplying J by the coordination number and it obviously results in a higher Tc but still a very different Tc from that reported in the article J was taken from.
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