Dear Dr. Bocan,<br> AS your input file suggest, you are not relaxing the system, you are doing the calculation for only one electronic cycle. As you have cleaved the bulk the atoms will relax upon cleaving and they wont be in the bulk-like position, so you must relax all of them. Put the flag "calculation" = "relax", it will minimize the forces and finally you will get the systems with atoms having force below the threshold value(you can use the default value in the code). And I think there is not need to use such a dense grid of k- points, I think 12x10x1 will suffice. <br>
<br><div class="gmail_quote">On Sat, Jun 11, 2011 at 8:05 AM, Gisela Bocan <span dir="ltr"><<a href="mailto:gbocan@gmail.com">gbocan@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Hello,<br> I assumed surface relaxation for the Ag(110) surface would be an easy matter. As it happens, I find non-zero forces parallel to the surface and therefore, upon relaxation, I get a non-neglectable parallel displacement of the ions. I am working with a 2x2sqrt(2) unit cell. I attach my <a href="http://file.in" target="_blank">file.in</a> and the forces I get. Note that the forces along one direction (x) are much larger that along the other one (y). Note as well the large values considered for ecutwfc, ecutrho, kpoints and the small degauss and conv_thr. Any ideas on how to correct this behaviour? Am I missing something? Thanks in advance and sorry if this is a stupid question. Small changes in the input parameters can lower the forces I get but I find nothing systematic. <br>
<br>&control<br> prefix = 't_G0',<br> outdir = ' ', <br> pseudo_dir = '/home/qe/pseudo', <br> calculation = 'scf',<br> tprnfor = .true.,<br> lkpoint_dir = .false.,<br>
verbosity = 'high',<br>/<br>&system<br> ibrav = 8,<br> celldm(1) = 11.1298607358762567,<br> celldm(2) = 1.4142135623730949,<br> celldm(3) = 2.25,<br> nat = 16,<br> ntyp = 1,<br>
ecutwfc = 45,<br> ecutrho = 450.00,<br> occupations = 'smearing', <br> smearing = 'mv', <br> degauss = 0.002, <br>/<br>&electrons<br> conv_thr = 1.d-12<br> diagonalization = 'cg'<br>
/<br>&ions<br>/<br>ATOMIC_SPECIES<br> Ag 107.8682 Ag.pbe-d-rrkjus.UPF <br>ATOMIC_POSITIONS crystal <br> Ag 0.0000000000000000 0.0000000000000000 0.3333333333333333 <br> Ag 0.5000000000000000 0.0000000000000000 0.3333333333333333 <br>
Ag 0.0000000000000000 0.5000000000000000 0.3333333333333333 <br> Ag 0.5000000000000000 0.5000000000000000 0.3333333333333333 <br> Ag 0.2500000000000000 0.2500000000000000 0.2222222222222222 <br>
Ag 0.7500000000000000 0.2500000000000000 0.2222222222222222 <br> Ag 0.2500000000000000 0.7500000000000000 0.2222222222222222 <br> Ag 0.7500000000000000 0.7500000000000000 0.2222222222222222 <br>
Ag 0.0000000000000000 0.0000000000000000 0.1111111111111111 <br> Ag 0.5000000000000000 0.0000000000000000 0.1111111111111111 <br> Ag 0.0000000000000000 0.5000000000000000 0.1111111111111111 <br>
Ag 0.5000000000000000 0.5000000000000000 0.1111111111111111 <br> Ag 0.2500000000000000 0.2500000000000000 0.0000000000000000 <br> Ag 0.7500000000000000 0.2500000000000000 0.0000000000000000 <br>
Ag 0.2500000000000000 0.7500000000000000 0.0000000000000000 <br> Ag 0.7500000000000000 0.7500000000000000 0.0000000000000000 <br>K_POINTS automatic<br> 33 23 1 0 0 0<br><br> atom 1 type 1 force = 0.00000000 0.00000000 -0.01175276<br>
atom 2 type 1 force = 0.00000000 0.00000000 -0.01175282<br> atom 3 type 1 force = 0.00000000 0.00000000 -0.01175318<br> atom 4 type 1 force = 0.00000000 0.00000000 -0.01175325<br>
atom 5 type 1 force = -0.00004221 0.00000033 0.01048323<br> atom 6 type 1 force = 0.00004221 0.00000033 0.01048323<br> atom 7 type 1 force = -0.00004221 -0.00000033 0.01048323<br>
atom 8 type 1 force = 0.00004221 -0.00000033 0.01048323<br> atom 9 type 1 force = 0.00000000 0.00000000 -0.01048309<br> atom 10 type 1 force = 0.00000000 0.00000000 -0.01048306<br>
atom 11 type 1 force = 0.00000000 0.00000000 -0.01048272<br> atom 12 type 1 force = 0.00000000 0.00000000 -0.01048269<br> atom 13 type 1 force = -0.00004148 0.00000003 0.01175266<br>
atom 14 type 1 force = 0.00004148 0.00000003 0.01175266<br> atom 15 type 1 force = -0.00004148 -0.00000003 0.01175266<br> atom 16 type 1 force = 0.00004148 -0.00000003 0.01175266<br>
<br>Dr. G. A. Bocan<br>Surface Physics Group, <br>Centro Atómico Bariloche, <br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>Regards,<br>MOHNISH,<br>-----------------------------------------------------------------<br>Mohnish Pandey<br>Senior Project Associate,<br>Department of Chemical Engineering,<br>
IIT KANPUR, UP, INDIA<br>-----------------------------------------------------------------<br>