# seeking advice for lammps software example from elastic and elastic_T

Dear friend,

even if some atoms are added or deleted in the geometric model, Do I haven’t to add the equilibration instructions to the procedure.Because it waste a massive of CPU time and is also unnecessary repetition. Besides, I have one more question about example elastic_T. The temperature is set 2000K in this example , but the results of the elastic constants show that the crystal structure is no longer cubic. In the exmple elastic, except for C11=C22=C33、C12=C13=C23、C44=C55=C66, the other constants are a minimal value that can be ignoredare, This result accords with the properties of cubic crystal. But in the example elastic_T , The rest of the elastic constant values reach the GPa order. What’s the reason? if you know, please tell me. Have a good day.

Dear friend,

even if some atoms are added or deleted in the geometric model, Do I haven't to add the equilibration instructions to the procedure.

i don't understand what you are asking here. you cannot change the
composition of the system during the evaluation of the elastic
constants.

Because it waste a massive of CPU time and is also unnecessary repetition. Besides, I have one more question about example elastic_T. The temperature is set 2000K in this example , but the results of the elastic constants show that the crystal structure is no longer cubic. In the exmple elastic, except for C11=C22=C33、C12=C13=C23、C44=C55=C66, the other constants are a minimal value that can be ignoredare, This result accords with the properties of cubic crystal. But in the example elastic_T , The rest of the elastic constant values reach the GPa order. What's the reason? if you know, please tell me. Have a good day.

you seem to be confusing the behavior that a system shows at finite
temperature with that at 0K. things are *much* more complex at finite
temperature (especially at elevated temperatures), as the system has
many equivalent states contributing to the ensemble and that need to
be considered/sampled, while at 0K you only have to consider a single
state (the minimum) and the curvature of the potential hypersurface
around it.

axel.