Dear all,<br><br>I want to calculate the binding energy for water adsorption at certain surface. So I first put an water molecule at some sites of the surface, and relaxed the whole systems( water and the upper half of the surface slab, lower slab was fixed). After  relax calculations finished, I copy the slab atoms and the water molecule coordinates separately into two inputfiles(the dimension of the supercell, and other parameters such as k point sampling, ecut, et al. were not changed) and performed a SCF calculation to get the single point energy. Then I substrated the two single point energy (water molecule and the surface slab) from the final energy for the whole system reported  by former relaxed calculation.<br>
this procedure was quite well when the adsorptions were in a molecular style. But if the water molecule dissociated at the surface, the subsequent SCF calculations of the dissociated water molecules were not converged. How could I cope with this? To increase the ecut, k-point, empty bands? to decrease the broadening,  mixing beta? Or setting the mixing mode to 'local-TF'? If the convergence could be achieved by doing this, do you think I could use the this value to calculate the  binding energy directly while the scf calculation of the slab and the former relax calculation were using different parameters (such as ecut, number of k-points,  mixing beta et al.)?<br clear="all">
<br>the input file of the scf calculation of water is show as follows (the water was in a dissociated configuration. and surface slab was  removed to perform scf calculation),<br><br> &CONTROL                                                                                 <br>
                       title = '*********_water' ,                                        <br>                 calculation = 'scf' ,                                                  <br>                restart_mode = 'from_scratch' ,                                           <br>
                      outdir = '/tmp/' ,   <br>                      wfcdir = '/tmp/' ,                                                  <br>                  pseudo_dir = '/home/vega/espresso-4.0/pseudo/' ,     <br>
                      prefix = '********_water' ,                                        <br>                     disk_io = 'none' ,                                                   <br>                       nstep = 1000 ,                                                     <br>
 /                                                                                        <br> &SYSTEM                                                                                  <br>                       ibrav = 8,                                                         <br>
                   celldm(1) =24.8624,<br>                   celldm(2) = 0.8520,<br>                   celldm(3) = 1.6964,<br>                         nat = 3,                                                       <br>                        ntyp = 2,                                                         <br>
                       nosym = .ture. ,                                                   <br>                   ecutwfc   =   30,<br>                   ecutrho   =  300,<br> /                                                                                        <br>
 &ELECTRONS                                                                               <br>                                                                     <br> /                                                                                                                    <br>
                                                 <br>ATOMIC_SPECIES <br># Ti   47.86700  Ti.pw91-sp-van_ak.UPF<br>    O   15.99940   O.pw91-van_ak.UPF<br>    H            1.00794   H.pw91-van_ak.UPF                                                    <br>
ATOMIC_POSITIONS crystal  <br>O       -0.672041076   0.333142157   0.526904777<br>H       -0.486792757   0.330778459   0.505140407<br>H       -0.739833562   0.333472512   0.544633120<br>K_POINTS gamma  <br><br>thank you for reading. <br>
<br>any hints on my questiosn will be deeply appreciated.<br><br>vega<br><br>-- <br>==================================================================================<br>Vega Lew ( weijia liu)<br>PH.D Candidate in Chemical Engineering<br>
State Key Laboratory of Materials-oriented Chemical Engineering<br>College of Chemistry and Chemical Engineering<br>Nanjing University of Technology, 210009, Nanjing, Jiangsu, China<br>******************************************************************************************************************<br>
Email: <a href="mailto:vegalew@gmail.com">vegalew@gmail.com</a><br>Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing, Jiangsu, China  <br>****************************************************************************************************************** <br>