Hi Gregorio,
SIESTA uses Voigt notation for stress / strain, namely s_11 --> s_1 s_22 --> s_2 s_33 --> s_3 s_23 --> s_4 s_13 --> s_5 s_12 --> s_6 Thus, writing %block GeometryConstraints stress 2 3 4 5 6 %endblock GeometryConstraints should be equivalent to putting all stresses to zero in constr.f but s_11. Regards, Roberto On Mon, 21 Dec 2009, [email protected] wrote:
Hi all I am trying to optimize a crystal with some constrains. I want only optimize cell sides, but no cell angles. For this, I add the next block label: %block GeometryConstraints stress 2 3 4 6 7 8 %endblock GeometryConstraints I thought that stress 1, 3 and 9 are correlated with axis a, b and c respectively (and unit cell vectors a11, a22 and a33). The remaining stress are corresponding to cell angles. I am sure that a11, a22, a33 are the cell side. Of this way, a12, a21, a22, a23, a32 and a33 positions of out cell are constants during the optimization. Does someone know the transformation matrix that SIESTA uses? I hope that you can understand me without problem Thank in advance Gregorio
