Hi<br>i am studying trying to relax the structure of Ni - Al system super cell with 40 atoms. what i understood till now is that if we don't specify nbnd it takes the defalt value. To test this i performed relax calculation with pure Ni with 1 atom first with out specifing any nbnd value then with nbnd = 10. the results were 6.66 equilibrium latt_parameter -2.62 kbar pressure and fermi energy 14.1765 for default nbnd and 6.66 equilibrium latt_parameter -2.5 kbar pressure and fermi energy 14.1765 for nbnd =10. there is slight change in the pressure value. why?<br>
<br>similar calculation i performed for the larger structure of Ni - Al system super cell with 40 atoms input file attached. but there is significant variation in the results. I have considered nbnd = 195 because i have 35 Ni and rest Al atoms.<br>
<br><font size="4"><b>condition (1)</b></font><br><font size="4"><b>INPUT</b></font><br>&SYSTEM<br>nspin = 2, starting_magnetization(1)=0.7<br>nbnd = 195<br><font size="4"><b>OUTPUT</b></font><br> total stress (Ry/bohr**3) (kbar) P= 3.59<br>
0.00002296 0.00000000 0.00000000 3.38 0.00 0.00<br> 0.00000000 0.00002296 0.00000000 0.00 3.38 0.00<br> 0.00000000 0.00000000 0.00002739 0.00 0.00 4.03<br>
<br> the Fermi energy is 13.5287 ev<br>! total energy = -3027.65131607 Ry<br> Harris-Foulkes estimate = -3027.65131529 Ry<br> estimated scf accuracy < 0.00000010 Ry<br><br>
The total energy is the sum of the following terms:<br><br> one-electron contribution = -1562.85025157 Ry<br> hartree contribution = 1281.18429645 Ry<br> xc contribution = -1063.08426181 Ry<br>
ewald contribution = -1682.87860135 Ry<br> smearing contrib. (-TS) = -0.02249780 Ry<br><br> total magnetization = 16.07 Bohr mag/cell<br> absolute magnetization = 19.19 Bohr mag/cell<br>
<br>ATOMIC_POSITIONS (crystal)<br>Ni 0.000000000 0.000000000 0.003462687<br>Ni 0.500000000 0.500000000 0.003077321<br>Ni 0.500000000 0.000000000 0.052355136<br>Ni 0.000000000 0.500000000 0.052355136<br>
Ni 0.000000000 0.000000000 0.101475754<br>Ni 0.500000000 0.500000000 0.101664051<br>Ni 0.500000000 0.000000000 0.150808385<br>Ni 0.000000000 0.500000000 0.150808385<br>Ni 0.000000000 0.000000000 0.200000000<br>
Ni 0.500000000 0.500000000 0.200000000<br><br><font size="4"><b>condition (2)</b></font><br>
<font size="4"><b>INPUT</b></font><br>
&SYSTEM<br>
nspin = 2, starting_magnetization(1)=0.7<br> <br>
<font size="4"><b>OUTPUT</b></font><br> total stress (Ry/bohr**3) (kbar) P= 2.93<br> 0.00001834 0.00000000 0.00000000 2.70 0.00 0.00<br> 0.00000000 0.00001834 0.00000000 0.00 2.70 0.00<br>
0.00000000 0.00000000 0.00002317 0.00 0.00 3.41<br> the Fermi energy is 13.5289 ev<br><br>! total energy = -3027.65133623 Ry<br> Harris-Foulkes estimate = -3027.65132967 Ry<br>
estimated scf accuracy < 0.00000007 Ry<br><br> The total energy is the sum of the following terms:<br><br> one-electron contribution = -1577.38934683 Ry<br> hartree contribution = 1288.44897083 Ry<br>
xc contribution = -1063.08376215 Ry<br> ewald contribution = -1675.60469092 Ry<br> smearing contrib. (-TS) = -0.02250718 Ry<br><br> total magnetization = 16.06 Bohr mag/cell<br>
absolute magnetization = 19.18 Bohr mag/cell<br>ATOMIC_POSITIONS (crystal)<br>Ni 0.000000000 0.000000000 0.003594618<br>Ni 0.500000000 0.500000000 0.003232516<br>Ni 0.500000000 0.000000000 0.052460864<br>
Ni 0.000000000 0.500000000 0.052460864<br>Ni 0.000000000 0.000000000 0.101507073<br>Ni 0.500000000 0.500000000 0.101682285<br>Ni 0.500000000 0.000000000 0.150774629<br>Ni 0.000000000 0.500000000 0.150774629<br>
Ni 0.000000000 0.000000000 0.200000000<br>Ni 0.500000000 0.500000000 0.200000000<br>Ni 0.500000000 0.000000000 0.249225371<br>Ni 0.000000000 0.500000000 0.249225371<br>Ni 0.000000000 0.000000000 0.298492927<br>
<br>there is significant variation in the stress, energy and the final coordinate of the atoms. i am not able to understand why it is getting size dependent. can anybody please help.<br><br>vicky singh<br><br>research student <br>
Bangalore<br>