<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">TO The Quantum Espresso Experts,<div><br></div><div>I was performing a convergence test for the cutoff energy of the SnO2 unit cell (Rutile) when I stumbled upon something odd during the 'vc-relax; runs. At some wfc cutoff energies QE does not find the proper symmetries, giving this error:</div><div><div>warning: symmetry operation # N not allowed. fractional translation:</div><div> 0.5000000 -0.5000000 0.5000000 in crystal coordinates</div></div><div>The program then proceeds to optimize the cell, but does not recognize its orthogonality and I end up with a parameter matrix that contains very small- but very present- off-diagonal elements.</div><div><br></div><div>Even stranger, the vc-relax calculation recognizes the symmetries and runs perfectly for a wfc cutoff of 30,35,40, and 55 Ry, but at 25, 45, and 50 Ry the symmetries aren't found. Also, my rho cutoff is 10*wfc for each of the calculations. (i.e. 30->300, 35->350, etc.)</div><div><br></div><div>I tried simplifying my coordinates, thinking that my precision was overkill, but that didn't work, and I am thinking it has to do with my pseudopotentials. I am using the O.pw91-van_ak.UPF included with QE for Oxygen, and Sn.pw91-n-van.UPF for Tin, which is downloadable from the QE site at: <a href="http://www.quantum-espresso.org/pseudo/1.3/html/Sn.html">http://www.quantum-espresso.org/pseudo/1.3/html/Sn.html</a></div><div><br></div><div>Right now I am continuing my studies with a wfc cutoff of 30Ry and a rho cutoff of 300Ry, since at this energy there was no issue with symmetries or bfgs convergence and the final parameters weren't that much different from the 55Ry calculation. However I am curious to know why these energies are causing problems with the symmetry finder.</div><div><br></div><div>Thank you for your time, </div><div><br></div><div>Daniel Cellucci</div><div>University of Georgia </div><div>Physics Department</div></body></html>