Hi,

I am doing some reading on the differences between doing a classic tension test and getting slope (as seen in tutorials) vs doing elastic script with 6 small deformations to get elastic constants. They do not predict the same values and I am not quite sure why. I have seen other papers compare the two methods, verifying that the do have a difference, but I am wondering why as they appear quite similar.

Thanks

Liam

Perhaps the slope method uses MD and the deformation method just uses molecular statics. Temperature matters.

Bruce

Morrissey, Liam S. <[email protected]…7202…> 于 2019年6月18日周二 22:19写道：

Yes, the static deformation uses molecular statics, but I am not totally sure what this means or how it is different from straining to 2% using fix deform and then taking slope of stress strain. I did a bit of research and I found this post below which seems to clear it up. The static uses energy minimizations to get properties and then calculates from that. Is this correct?

Thanks very much for your help!

“In my view, better way to calculate elastic properties is to use static analysis, which you can do with a very small system size. Use energy minimization to get the system properties (energy, pressures, dimensions, etc) for deformed and un-deformed state and calculate elastic constants from there.”

When correctly done, the finite-temperature (molecular dynamics) results should converge to the zero-temperature (molecular statics) results in the limit of low temperature. Elastic constants are usually weakly dependent on temperature. A strain rate of 2% might be too large to get the accurate elastic constants. In molecular statics, one usually uses up to 0.5% strain to fit the energy-strain curves or the stress-strain curves. It is also important to fully equilibrate (or relax) the structure before measuring the energy-strain or stress-strain curves. Anyway, the two methods should be equivalent at low temperatures.

Bruce