How to calculate the Neel temperature

[Yu Xie]

Hello vampire users,

I'm Yu Xie from ORNL.

I'm interested in the Neel temperature of some 2D AFM materials. It has been shown in the features that Vampire can calculate it. But I can't find any useful information from the tutorial and the manual. Can anyone say/show an example for it?

Thanks in advance.

Best regards,

Yu

[Muftah Al-Mahdawi]

Hello Yu,

For that you need to define your AFM as a set of materials, one for each sublattice. So Vampire can calculate thermal averages for each specific one.

Attached is a somehow a simplified example for CoO. CoO seems not that simple.

The crystal structure part of UCF file has a place to choose material from MAT file. The choice should be so that each material correspond to a sublattice.
The output file will have the average magnetization of each material.

Regards,
Muftah

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[Yu Xie]

Dear Muftah,

Thanks for your detailed response! It's really helpful.

If I understand correctly, the sublattice of the materials means I need to separate the spin up and spin down atoms. Is it right?

I'll try to run the example you attached.

Thank you again.

Best, Yu

在 2016年4月1日星期五 UTC+8下午2:54:56，Muftah Al-Mahdawi写道：

[Gargee Bhattacharyya]

Hi Yu Xie,

    I am new to this group. I am trying to calculate Neel temperature of AFM materials (2D material). I have seen the input file for curie temperature calculation and also for Neel temperature calculation. I have some questions. 

1. What is the meaning of the " You need to define your AFM as a set of materials, one for each sublattice. So Vampire can calculate thermal averages for each specific one." ? Suppose , I have graphene sheet with one atom doped in a supercell of graphene. For the calculation of exchange parameter  I am using 2 * 2 supercell containing 4 doped atoms. Please specify how I will specify my input ?

2. The input file of Neel temperature calculation of CoO contains a tag 

#------------------------------------------

# Program and integrator details

#------------------------------------------

sim:program=curie-temperature

sim:integrator=monte-carlo

and at the temperature section they wrote 

#------------------------------------------

# Simulation attributes:

#------------------------------------------

sim:minimum-temperature=150

sim:maximum-temperature=350

sim:temperature-increment=5 

How the minimum and maximum temperature is chosen ?  Should I write "curie-temperature" while calculating Neel temperature also ? 

3. Please explain the interaction type in the .UCF file , what does the parameters dx, dy and dz signify ? Please explain the parameters mentioned here. 

#Interactions n exctype, id i j dx dy   dz        Jij

48 0

0 0 2 0 -1 -1 -9.04E-021

1 0 3 -1 0 -1 -9.04E-021

2 0 2 0 0 -1 -9.04E-021

3 0 3 0 0 -1 -9.04E-021

4 0 1 -1 -1 0 -9.04E-021

5 0 1 0 -1 0 -9.04E-021

6 0 2 0 -1 0 -9.04E-021

7 0 1 -1 0 0 -9.04E-021

8 0 3 -1 0 0 -9.04E-021

9 0 1 0 0 0 -9.04E-021

10 0 2 0 0 0 -9.04E-021

11 0 3 0 0 0 -9.04E-021

12 1 2 0 0 -1 -9.04E-021

13 1 3 0 0 -1 -9.04E-021

14 1 2 1 0 -1 -9.04E-021

15 1 3 0 1 -1 -9.04E-021

16 1 0 0 0 0 -9.04E-021

17 1 2 0 0 0 -9.04E-021

18 1 3 0 0 0 -9.04E-021

19 1 0 1 0 0 -9.04E-021

20 1 2 1 0 0 -9.04E-021

21 1 0 0 1 0 -9.04E-021

22 1 3 0 1 0 -9.04E-021

23 1 0 1 1 0 -9.04E-021

24 2 1 -1 0 0 -9.04E-021

25 2 3 -1 0 0 -9.04E-021

26 2 0 0 0 0 -9.04E-021

27 2 1 0 0 0 -9.04E-021

28 2 3 0 0 0 -9.04E-021

29 2 3 -1 1 0 -9.04E-021

30 2 0 0 1 0 -9.04E-021

31 2 3 0 1 0 -9.04E-021

32 2 1 -1 0 1 -9.04E-021

33 2 0 0 0 1 -9.04E-021

34 2 1 0 0 1 -9.04E-021

35 2 0 0 1 1 -9.04E-021

36 3 1 0 -1 0 -9.04E-021

37 3 2 0 -1 0 -9.04E-021

38 3 2 1 -1 0 -9.04E-021

39 3 0 0 0 0 -9.04E-021

40 3 1 0 0 0 -9.04E-021

41 3 2 0 0 0 -9.04E-021

42 3 0 1 0 0 -9.04E-021

43 3 2 1 0 0 -9.04E-021

44 3 1 0 -1 1 -9.04E-021

45 3 0 0 0 1 -9.04E-021

46 3 1 0 0 1 -9.04E-021

47 3 0 1 0 1 -9.04E-021

But for the calculation of curie temperature the exchange interactions are 

# Interactions n exctype, id i j dx dy dz Jij

4 1

0 0 0 1 0 0 4.85e-21

1 0 0 -1 0 0 4.85e-21

2 0 0 0 1 0 4.85e-21

3 0 0 0 -1 0 4.85e-21

Please explain it .