[Q-e-developers] the sign of expression for force

[Paolo Giannozzi]

Forces are forces, that is, -dE/dR. You can easily verify that by taking
fcc Si, displacing one atom (or both atoms) along (111) and looking at the
direction of forces

Paolo

On Sun, Nov 1, 2015 at 12:53 PM, Jiqiang Li <jqli14 at fudan.edu.cn> wrote:

> Dear all,
>        Physically force can be denoted by F(R)= - dE/dR, and
> Helleman-Feyman theory is employed in DFT to evaluate force. In numerical
> routine of Pwscf code, does  force equal -dE/dR or dE/dR?
>
> Jiqiang Li
>
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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