how to get mechanical constant

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dyc_2008 · #1 Post by **dyc_2008** » Fri Oct 15, 2010 4:59 am

dear all：
after relaxation。I get the optimistic supercell。so how to get any mechanical constant at a given direction。such as strain tensor。
<span class='smallblacktext'>[ Edited ]</span>

riche · #2 Post by **riche** » Tue Oct 19, 2010 9:43 am

Dear dyc_2008,
Could you please make your question specific?
What do you mean by mechanical constants? What do you need strain tensor for?

dyc_2008 · #3 Post by **dyc_2008** » Tue Oct 19, 2010 2:12 pm

may be i have used wrong words â€˜strain tensor â€™。
i just want to compare the elastic behavior of two materials。

riche · #4 Post by **riche** » Tue Oct 19, 2010 4:15 pm

Then just calculate the elastic constants.

forsdan · #5 Post by **forsdan** » Tue Oct 19, 2010 5:43 pm

@dyc_2008: If you have access to vasp 5.2, then you can use IBRION=6 and ISIF>= 3 to calculate elastic constants. Please see the manual

http://cms.mpi.univie.ac.at/vasp/vasp/I ... ION_6.html

Otherwise you will have to resort to the standard strain-stress or energy-strain relationships for your structure, and evaluate them by yourself by using several supercell calculations.

Cheers,
/Dan