Relaxation of devices using the OptimizeDeviceConfiguration

[asma]

I built my device , then I noticed that I need to perform device relaxation. So I'm following the steps in the below link:
https://docs.quantumwise.com/tutorials/optimize_device_configuration/optimize_device_configuration.html

My questions are:
Why do we need to relax the device?
The papers I'm using as a reference are using DFT for device relaxation which is taking a looong time and not even finishing?!
Using ATK forcefield gave me quick relaxed device?
How can I make sure that my device relaxation is correct?

Thanks

[Petr Khomyakov]

Strain in devices may affect their properties, this is why one needs a device in its relaxed, equilibrium state. You have to compute forces acting on individual atoms to see if they are small enough. The latter certainly means that you have to set tolerance for forces that you think is acceptable. 

[asma]

I got it. Thanks for your reply.