Quantum Espresso Optimization

[cm]

Hi,
I’m confused with the QE syntax for optimization.

1. What’s the difference between calculation=’relax’ and calculation=’vc-relax’? What other changes do we have to do in the cif file to run such computation?

2. In what case do we have to put the field press to 0.5 in &CELL and when do we have to put that field equal to the stress tensor mean value?

As I understand it:
– relax = only optimization of atomic position => mediumly computational expensive (what we have to perform in “step 3: position optimization”)
– vc-relax: lattice, angular parameters and atomic positions optimized => very computational expensive (what we have to perform in “full optimization”). Here “press” in &CELL = ?

Thank you!

CM

[Stefaan Cottenier]

This will be summarized once more at the end of the feedback webinar.

relax ==> only internal positions are optimized, the cell shape and volume is frozen
vc-relax ==> internal positions as well as cell shape and size are optimized.

The CELL block is for vc-relax only. It specifies the target pressure (often that will be zero, but you could want to find the cell shape and size at other pressures as well). In cases where the pressure at the end of the scf cycle does not agree with what you asked for, you’ll have to do another round (which may include setting the press variable to a new value, if you aim for the pressure that corresponds to a user-defined volume range).

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