<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div>Dear all,<br></div><div><br data-mce-bogus="1"></div><div>I'm currently running calculations with simple linear molecules (for example : hydrogen cyanide <!--StartFragment--><!--EndFragment-->HCN) adsorbed on graphene+metal surface.<br data-mce-bogus="1"></div><div>Surprinsigly, I faced few issues concerning the relaxation of these structures. Sometimes the molecules can not relax without forming an angle around 140° instead of 180° as expected.<br></div><div><br data-mce-bogus="1"></div><div>In order to fix this I used the CONSTRAINTs tag as shown here :<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>CONSTRAINTS<br>1 1.5<br>'planar_angle' 33 34 35<br><br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>The 33, 34 and 35 atoms being the concerned atom. Even with the constraints it is sometimes impossible to obtain a logical relaxed structures with an angle around 180°.</div><div>And sometimes the calculation are even crashing with the message " g = 0 is not satified ".<br></div><div>I have read the doc about constraints of pw.x but nothing indicates me the way to resolve this.<br data-mce-bogus="1"></div><div>Also I would like to understang how the parameter CONSTR_TOL (equal to 1.5 in the example) affects the calculations (nothing in the doc about this point) ?<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Thanks<br data-mce-bogus="1"></div><div>-- <br></div><div>Julien Claudot<br>Post-doc <br></div><div>IGCM UMR5253<br data-mce-bogus="1"></div><div>DAMP team<br data-mce-bogus="1"></div></div></body></html>