<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi,<div>I started looking at wannier90 recently. First of all, many thanks to the developers for making available such a wonderful tool.</div><div>While going through the examples I found one problem I would like to comment on.</div><div>It must be related with handling finite differences from k-points for large supercells.</div><div>If one modifies example 10 for graphite to have a larger unit cell size in the z direction it automatically separates further the layers and the bands</div><div>become that of graphene.</div><div>By modifying accordingly the energy windows I can reproduce the bands for graphene reported in your accepted RMP paper.</div><div>The recipe of eliminating one of the carbon layers and separating the layers also gives essentially the same band structure of graphene.</div><div>The problem starts when the z-axis cell size becomes too large. When the inter-graphene layer distances are greater than about 8 angstroms</div><div>you start noticing that the center of the initial projections of the pz orbitans are slightly out of plane.</div><div><br></div><div><br></div><div>To illustrate my point I copy below the relevant regions of graphite.wout for two cases.</div><div>One is for graphite with Lz = 16 angstroms, this is 8 angstroms separation between layers</div><div>and another for Lz = 20 angstroms. You can notice that already for Lz=16 angstroms it starts to show</div><div>tiny out of plane displacements of the pz (or sigma) orbital projections from the planes that become notoriously larger when Lz=20 angstroms.</div><div><br></div><div><br></div><div>Lz = 16 angstroms (200 iterations)</div><div><div><div> ------------------------------------------------------------------------------</div><div> Initial State</div><div> WF centre and spread 1 ( -0.352578, 0.610683, 12.000001 ) 0.60267243</div><div> WF centre and spread 2 ( -0.352578, -0.610683, 12.000000 ) 0.60267233</div><div> WF centre and spread 3 ( 0.705155, 0.000000, 12.000001 ) 0.60267249</div><div> WF centre and spread 4 ( 0.000000, 0.000000, 11.999996 ) 1.03588860</div><div> WF centre and spread 5 ( 0.357562, 1.840684, 4.000000 ) 0.60267395</div><div> WF centre and spread 6 ( 0.357559, 0.619314, 4.000000 ) 0.60267487</div><div> WF centre and spread 7 ( 1.415300, 1.230002, 4.000000 ) 0.60267488</div><div> WF centre and spread 8 ( 0.710140, 1.230000, 4.000015 ) 1.03634288</div><div> WF centre and spread 9 ( 0.000000, 0.000000, 4.000006 ) 1.03588731</div><div> WF centre and spread 10 ( -0.710140, -1.230000, 11.999980 ) 1.03634402</div><div> Sum of centres and spreads ( 2.130421, 3.690000, 79.999997 ) 7.76050374</div><div> </div><div> 0 0.776E+01 0.0000000000 7.7605037421 6.36 <-- CONV</div><div> O_D= 0.2585153 O_OD= 1.5936799 O_TOT= 7.7605037 <-- SPRD</div></div></div><div><br></div><div><div><div><br></div><div> Writing checkpoint file graphite.chk... done</div><div><br></div><div> Final State</div><div> WF centre and spread 1 ( -0.355069, 0.614998, 12.000030 ) 0.54986868</div><div> WF centre and spread 2 ( -0.355069, -0.614998, 12.000031 ) 0.54986863</div><div> WF centre and spread 3 ( 0.710139, 0.000000, 12.000031 ) 0.54986870</div><div> WF centre and spread 4 ( 0.000000, 0.000000, 11.999956 ) 1.03587760</div><div> WF centre and spread 5 ( 0.355069, 1.845001, 3.999973 ) 0.54986870</div><div> WF centre and spread 6 ( 0.355069, 0.614998, 3.999974 ) 0.54986865</div><div> WF centre and spread 7 ( 1.420283, 1.229999, 3.999973 ) 0.54986864</div><div> WF centre and spread 8 ( 0.710140, 1.229999, 4.000062 ) 1.03633230</div><div> WF centre and spread 9 ( 0.000000, 0.000000, 4.000038 ) 1.03587875</div><div> WF centre and spread 10 ( -0.710140, -1.229999, 11.999930 ) 1.03633257</div><div> Sum of centres and spreads ( 2.130422, 3.689998, 79.999997 ) 7.44363322</div><div> </div><div> Spreads (Ang^2) Omega I = 5.908308580</div><div> ================ Omega D = 0.020570360</div><div> Omega OD = 1.514754280</div><div> Final Spread (Ang^2) Omega Total = 7.443633219</div><div> ------------------------------------------------------------------------------</div><div> Time for wannierise 3.627 (sec)</div></div></div><div><br></div><div>---------</div><div><br></div><div><br></div><div>Lz = 20 angstroms</div><div><br></div><div><div> ------------------------------------------------------------------------------</div><div> Initial State</div><div> WF centre and spread 1 ( -0.349901, 0.598862, 14.995413 ) 0.62617014</div><div> WF centre and spread 2 ( -0.347302, -0.612222, 14.998605 ) 0.61406608</div><div> WF centre and spread 3 ( 0.695169, -0.009180, 14.993375 ) 0.64937494</div><div> WF centre and spread 4 ( 0.000002, -0.000002, 14.706700 ) 17.86025818</div><div> WF centre and spread 5 ( 0.358160, 1.838524, 5.001654 ) 0.61232466</div><div> WF centre and spread 6 ( 0.360228, 0.628444, 5.008041 ) 0.65266434</div><div> WF centre and spread 7 ( 1.411733, 1.231610, 5.001470 ) 0.60771954</div><div> WF centre and spread 8 ( 0.710141, 1.229999, 4.735334 ) 15.16970546</div><div> WF centre and spread 9 ( 0.000001, -0.000001, 4.752679 ) 14.71429866</div><div> WF centre and spread 10 ( -0.710141, -1.230001, 14.707123 ) 17.71804348</div><div> Sum of centres and spreads ( 2.128092, 3.676033, 98.900394 ) 69.22462547</div><div> </div><div> 0 0.692E+02 0.0000000000 69.2246254748 6.35 <-- CONV</div><div> O_D= 29.7816077 O_OD= 32.8026254 O_TOT= 69.2246255 <-- SPRD</div></div><div><br></div><div><div> Final State</div><div> WF centre and spread 1 ( -0.355898, 0.615907, 15.047911 ) 0.55389069</div><div> WF centre and spread 2 ( -0.356443, -0.615759, 15.029877 ) 0.55225267</div><div> WF centre and spread 3 ( 0.711527, 0.000548, 15.020749 ) 0.55177652</div><div> WF centre and spread 4 ( -0.000694, -0.000132, 14.966088 ) 1.24801183</div><div> WF centre and spread 5 ( 0.354420, 1.846537, 4.957860 ) 0.55345004</div><div> WF centre and spread 6 ( 0.354167, 0.613572, 4.967165 ) 0.55287958</div><div> WF centre and spread 7 ( 1.421761, 1.230258, 4.961887 ) 0.55318423</div><div> WF centre and spread 8 ( 0.710343, 1.230548, 5.043238 ) 1.16093772</div><div> WF centre and spread 9 ( -0.000472, -0.002028, 5.154334 ) 1.60886377</div><div> WF centre and spread 10 ( -0.708131, -1.229836, 14.867101 ) 1.50509444</div><div> Sum of centres and spreads ( 2.130578, 3.689615,100.016210 ) 8.84034150</div><div> </div><div> Spreads (Ang^2) Omega I = 6.640392353</div><div> ================ Omega D = 0.188848567</div><div> Omega OD = 2.011100578</div><div> Final Spread (Ang^2) Omega Total = 8.840341498</div><div> ------------------------------------------------------------------------------</div><div> Time for wannierise 3.767 (sec)</div><div><br></div><div> Writing checkpoint file graphite.chk... done</div></div><div><br></div><div><br></div><div>Actually there is a previous email from a Chinese fellow last month showing results for graphene with interlayer separation of </div><div>10 Angstroms and you can notice this small effect in his results too. </div><div>This should be the reason for his antibonding pi bands looking different from the results in RMP paper outside the inner window.</div><div><br></div><div>My questions are:</div><div>1. Why are the initial projections of the wannier functions not centered exactly at the same z values like in normal graphite?</div><div><br></div><div>2. Why the localization procedure fails to bring them back in plane? I believe this question is related with 1.</div><div><br></div><div>3. How to foresee when this type of problems can happen in supercell calculations of slab geometries?</div><div>It certainly would be problematic if a DFT calculation can provide the inputs but for some reason wannier90.x cannot cope</div><div>with systems that have large vacuum spacing between the slabs. </div><div><br></div><div><br></div><div>From a more practical point of view, my question would be what to change in an example case of</div><div>graphite with Lz = 30 angstroms to prevent the centers from moving out of the plane? The input files would be essentially the same as</div><div>that provided with the codes but changing Lz = 30 and changing the energy windows. Another change was that I used norm conserving instead of ultrasoft.</div><div><div>I tried changing several other parameters, like increasing the density of in plane kx, ky, points to balance the weights</div><div>of the b vectors and their anisotropy but this did not have any effect. Switching on and off guiding_centres flag didn't do anything either.</div><div>Increasing the number of kz further increases the weight imbalance between the</div><div>b vectors but sometimes seemed to improve the final results but never completely and could not see any systematic behavior.</div><div>At times I needed to modify the 'search_shells' parameter to a larger number when very large Lz were used.</div><div>I haven't tried but I don't think that changing '<span class="Apple-style-span" style="color: rgb(26, 26, 24); font-size: 12px; ">dist cutoff mode' nor the specification of the '</span><span class="Apple-style-span" style="color: rgb(26, 26, 24); font-size: 12px; ">one dim axis</span><span class="Apple-style-span" style="color: rgb(26, 26, 24); font-size: 12px; ">' should be the solutions either.</span></div><div>The only clear thing I could conclude from trying different parameters was that when Lz becomes large enough, in this case larger than about 8 angstroms, the results start to go wrong.</div></div><div>However, from symmetry considerations I can't see why they should shift the wave functions centers.</div><div>Any insightful comment would be welcome.</div><div>Thanks,</div><div>Jeil</div><div><br></div><div><br></div></body></html>