Asymmetric exchange interactions in local unit cell error.

[Isa Tristan Lough]

Dear Dr. Evans and other VAMPIRE users,

I am attempting to do a CMC anisotropy calculation using my own custom .ucf file for an FCC antiferromagnetic 3d oxide. I have followed the scheme provided in the VAMPIRE manual, that is, where dx, dy and dz values of (0, 0, 0) define the interactions in the local unit cell. The cubic unit cell has eight atoms with the magnetic atoms sitting at the vertices of a tetrahedron (1,2,3,4), I have shown a diagram below.

                                        

                 X---------------2

                  |                   |

                  |                   |

       1----------------X       |

        |         |         |         |

        |        3------- |-------X

        |                   |

        |                   |

       X---------------4

To define the nearest neighbour interactions in my local unit cell I have included the following interactions in my .ucf file:

    i     j     dx    dy    dz      Jij

    1    4    0      0      0

    1    2    0      0      0

    4    2    0      0      0

    4    3    0      0      0

    3    2    0      0      0

    3    1    0      0      0

Which are all the nearest neighbour interactions I would expect in the local unit cell, everytime I try to run VAMPIRE I receive the following error message:

Error! Exchange interaction list in unit cell file .ucf contains the following assymetric interactions:

and the six exchange interactions I have listed above are printed out. I am not sure why VAMPIRE interprets these as asymmetric interactions, and I am struggling to figure out how to deal with this error. I realise that I could use 'create:crystal-structure = fcc' instead, but I intend to use the .ucf file for defining custom exchange interactions in my unit cells for the future  Any help would be greatly appreciated!

Regards,

Isa Lough

UCL Dept. of Materials Chemistry

[Sarah Jenkins]

Hey Isa, 

Vampire is coming up with this error because you need to define your interactions both ways: so 1 interacts with 4 and 4 interacts with 1, that is why it is saying that the interactions are asymmetric. If you double your interactions list and flip i and j it. should work!

Best wishes,
Sarah

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[Isa Tristan Lough]

Hi Sarah,

I see, thanks alot!

Isa

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