<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div style="RIGHT: auto">Dear users,</div>
<div style="RIGHT: auto"> In "WIEN2k-FAQ: KGEN: Add inversion ? Shift k-mesh ?"</div>
<LI style="RIGHT: auto"><B>"shift"the k-mesh ? </B>(only for some lattice types)
<UL style="RIGHT: auto">
<LI style="RIGHT: auto">"Shifting" of k-mesh means that it will add (x,x,x) to all generated k-points, thus shifting them from high symmetry points (lines) to more "general" points with a higher weight. By this procedure (known also as <B style="RIGHT: auto">"special k-point methods"</B>) one generates an equally "dense" mesh, but with less basis points.
<LI>Usually a shift is <B>recommended </B>. Only one word of warning: When you are interested in "gaps" of semiconductors, they are often located at Gamma or X (or at some other BZ-border point). With shifted meshes you will NOT have those high-symmetry points in your mesh, thus the gap may seem to be smaller/larger than expected.
<LI style="RIGHT: auto">Solution to this problem: Do the scf cycle with the shifted mesh, but for a DOS change to a fine unshifted mesh. </LI></UL></LI>
<div style="RIGHT: auto">From that we know that shifting of k-mesh generates an equally 'dense' mesh. So we should get nearly the same results for the same case whether shift k-mesh or not.</div>
<div style="RIGHT: auto">I calculated the same case (TiO2 2*2*2 supercell) with shift k-mesh and no shift k-mesh. But the ENE are different.</div>
<div style="RIGHT: auto">grep :ENE 222.scf_mini (shift k-mesh? Yes)<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63765571<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63322019<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63804051<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63815033<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63855011</div>
<div style="RIGHT: auto"> </div>
<div style="RIGHT: auto">grep :ENE 222.scf_mini(shift k-mesh? No)<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63642529<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63182990<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63679565<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63690506<BR>:ENE : ********** TOTAL ENERGY IN Ry = -32144.63730723<BR></div>
<div style="RIGHT: auto">The energies are different widely. I can not understand. </div>
<div style="RIGHT: auto">For other case i minimized the struct with shift k-mesh and then run a cycle with no shift k-mesh, the energy may be larger or smaller. And the forces are not smaller than 2.</div>
<div style="RIGHT: auto">Can you explain it for me? Thank you for your time and patience<VAR id=yui-ie-cursor></VAR>.</div>
<div style="RIGHT: auto">yours sincerely,</div>
<div style="RIGHT: auto">Hongxia Wang</div></div></body></html>