<div>Hi,</div>
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<div>I am trying to calculate surface energy of MgO surface layers using PWSCF. For that i have used 2 methods given as </div>
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<div>1)Ens={En-n(En-En-1)}/2A</div>
<div> here n=no of layers, En and En-1 are total energies of n and n-1 layers, A=surface area of primitive cell</div>
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<div>2)Ens=(En-mEbulk)/2A</div>
<div> here m=no of primitive units present in surface, Ebulk=total energy of primitive unit cell</div>
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<div>I have got converged surfae energy 0.004au/bohr**2 by using method 1, but by using method 2 i got very different energies and not converged by varying number of layers. When i checked with xcrysden the periodic repetetion in primitive cell is not good. Initially i have followed by cartesian coordinates but the number of symmetry operations observed as 1, but when followed by fractional coordinates symmetry operations are 48 now.</div>
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<div><span lang="EN"> MgO conventional cell is in FCC bravis lattice group and i have used the following input for the primitive cell description
<p><font color="#ff6666">&SYSTEM</font></p>
<p><font color="#ff6666">ibrav = 2,</font></p>
<p><font color="#ff6666">A = 2.977768,</font></p>
<p><font color="#ff6666">B = 2.977768,</font></p>
<p><font color="#ff6666">C = 2.977768,</font></p>
<p><font color="#ff6666">cosAB = 0.5,</font></p>
<p><font color="#ff6666">cosAC = 0.5,</font></p>
<p><font color="#ff6666">cosBC = 0.5, </font></p>
<p><font color="#ff6666">nat = 2,</font></p>
<p><font color="#ff6666">ntyp = 2,</font></p>
<p><font color="#ff6666">ecutwfc = 25,</font></p>
<p><font color="#ff6666">ecutrho = 200,</font></p>
<p><font color="#ff6666">/</font></p>
<p><font color="#ff6666">&ELECTRONS</font></p>
<p><font color="#ff6666">electron_maxstep = 500,</font></p>
<p><font color="#ff6666">diago_david_ndim = 6, </font></p>
<p><font color="#ff6666">/</font></p>
<p><font color="#ff6666">&IONS</font></p>
<p><font color="#ff6666">ion_dynamics = 'bfgs',</font></p>
<p><font color="#ff6666">/</font></p>
<p><font color="#ff6666">ATOMIC_SPECIES</font></p>
<p><font color="#ff6666">O 16.000 O.pw91-van_ak.UPF </font></p>
<p><font color="#ff6666">Mg 24.305 Mg.pw91-np-van.UPF</font></p>
<p><font color="#ff6666">ATOMIC_POSITIONS crystal </font></p>
<p><font color="#ff6666">Mg 0.00000000 0.00000000 0.00000000</font></p>
<p><font color="#ff6666">O 0.50000000 0.50000000 0.50000000</font></p>
<p><font color="#ff6666">K_POINTS automatic </font></p>
<p><font color="#ff6666">4 4 4 0 0 0</font> </p>
<p> </p></span></div>
<div>Please suggest me where i have done mistake and thanks in advance</div>
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<div>G. Krishna Chaitanya</div>
<div>Senior research fellow</div>
<div>C/o Dr. Bhanuprakash K.</div>
<div>Inorganic Chemistry Division</div>
<div>Indian Institute of Chemical Technology</div>
<div>Hyderabad, India</div>
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