<div dir="ltr"><div>Dear all<br>I am trying to calculate the binding energy for DNA 
adsorption on 2D 
sheets.I have done calculation by including vdW correction and simple 
PBE calculation with Ultrasoft pseudopotential. While studying the 
adsorption of the four nitrogen bases on the 
2D surface I have observed that the binding energy for the cytosine 
adsorption on surface is coming out to be very different (almost three 
times larger) from what is 
expected when I include the vdW correction (vdw_corr = 'DFT-D') in to
 the calculations. Whereas, when I do only with PBE (no vdW correction) 
all the four bases gives expected correct energies.The parameters which 
has been included for vdW correction are as follows<br>      &SYSTEM<br>                       ibrav = 0,<br>                    celldm(1)= 1.89 ,<br>                         nat = 88,<br>                        ntyp = 5,<br>                    vdw_corr = 'DFT-D',<br>                      london = .TRUE.,<br>                     ecutwfc = 50 ,<br>                     ecutrho = 500 ,<br>                 occupations = 'smearing' ,<br>                    smearing = 'gaussian' ,<br>                     degauss = 0.020<br>/<br>&ELECTRONS<br>            electron_maxstep = 500 ,<br>                    conv_thr = 1.0d-5 ,<br>                 mixing_mode = 'plain' ,<br>                 mixing_beta = 0.7 ,<br>             diagonalization = 'david' ,<br>/<br><span id="gmail-m_2020564517703286188gmail-:ej.co" class="gmail-m_2020564517703286188gmail-tL8wMe gmail-m_2020564517703286188gmail-EMoHub" style="text-align:left" dir="ltr">Please
 help me with this unexpected value of the binding energy value for the 
cytosine? Any kind of help would be appreciated.<br><br><br></span><br><br></div>Thank you<br>Amita Sihag<br>Research Student, Dept. of Chemistry<br>Indian Institute of Technology Gandhinagar<br>Gujrat (India)<span class="gmail-HOEnZb gmail-adL"></span></div>