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<P>Dear All,</P>
<P> </P>
<P>I am a newer to use Quantum Espresso. Could you please do me a favor to answer some little questions I met when using Quantum Espresso? </P>
<P> </P>
<P>1. I am investigating the BaTiO3 crystal and used the best optimized parameter a=7.5344 Bohr. I used 'scf' to calculate the total energy. However, I obtained different values when using different number of cells. For example, when I use the unit cell, the total energy is -304 Ry, but when I use 1X1X2 supercell, I obtained E=-598Ry, i.e., -299Ry per unit cell, when I increased to 2X2X4 supercell (the input file is below these questions), I got E=-4766Ry, i.e., -298 Ry per unit cell. What is wrong?</P>
<P> </P>
<P>2. Another strange result is when I replaced two Ti atoms (Ti4+) by two Fe atoms (Fe3+) and removed one O atom (O2-) between them in the 2X2X4 supercell, I obtained even lower energy than the pure BaTiO3 crystal. What is wrong? It isnot reasonable, right?</P>
<P> </P>
<P>3. I use the atom pseudopotential file, but Ba4+ or Fe3+ are both ions, should I generate their ionic pseudopotential files?</P>
<P> </P>
<P>Following is my input file.</P>
<P> </P><SPAN lang=EN>
<P>&control</P>
<P>calculation = 'scf',</P>
<P>prefix = 'BaTiO3',</P>
<P>pseudo_dir='/work/01553/geng'</P>
<P>/</P>
<P>&system</P>
<P>degauss=0.01</P>
<P>ibrav=6</P>
<P>celldm(1)=15.0688</P>
<P>celldm(3)=2</P>
<P>nat=80</P>
<P>ntyp=3</P>
<P>ecutwfc=30.0</P>
<P>ecutrho=300.</P>
<P>/</P>
<P>&electrons</P>
<P>conv_thr = 1e-5,</P>
<P>mixing_beta=0.7</P>
<P>/</P>
<P>&IONS</P>
<P>ion_dynamics='bfgs',</P>
<P>/</P>
<P>&CELL</P>
<P>cell_dynamics='damp-w',</P>
<P>/</P>
<P>ATOMIC_SPECIES</P>
<P>Ba 137.327 Ba.pbe-nsp-van.UPF</P>
<P>Ti 47.867 Ti.pbe-sp-van_ak.UPF</P>
<P>O 15.9994 O.pbe-van_ak.UPF</P>
<P> </P>
<P>ATOMIC_POSITIONS</P>
<P> </P>
<P>Ba 0.000 0.000 0.000</P>
<P>Ba 0.000 0.000 0.250</P>
<P>Ba 0.000 0.000 0.500</P>
<P>Ba 0.000 0.000 0.750</P>
<P>Ba 0.500 0.000 0.000</P>
<P>Ba 0.000 0.500 0.000</P>
<P>Ba 0.500 0.500 0.000</P>
<P>Ba 0.500 0.000 0.250</P>
<P>Ba 0.500 0.000 0.500</P>
<P>Ba 0.500 0.000 0.750</P>
<P>Ba 0.000 0.500 0.250</P>
<P>Ba 0.000 0.500 0.500</P>
<P>Ba 0.000 0.500 0.750</P>
<P>Ba 0.500 0.500 0.250</P>
<P>Ba 0.500 0.500 0.500</P>
<P>Ba 0.500 0.500 0.750</P>
<P></P>
<P>Ti 0.250 0.250 0.125</P>
<P>Ti 0.250 0.250 0.375</P>
<P>Ti 0.250 0.250 0.625</P>
<P>Ti 0.250 0.250 0.875</P>
<P>Ti 0.750 0.250 0.125</P>
<P>Ti 0.750 0.250 0.375</P>
<P>Ti 0.750 0.250 0.625</P>
<P>Ti 0.750 0.250 0.875</P>
<P>Ti 0.250 0.750 0.125</P>
<P>Ti 0.250 0.750 0.375</P>
<P>Ti 0.250 0.750 0.625</P>
<P>Ti 0.250 0.750 0.875</P>
<P>Ti 0.750 0.750 0.125</P>
<P>Ti 0.750 0.750 0.375</P>
<P>Ti 0.750 0.750 0.625</P>
<P>Ti 0.750 0.750 0.875</P>
<P>O 0.250 0.000 0.125</P>
<P>O 0.250 0.000 0.375</P>
<P>O 0.250 0.000 0.625</P>
<P>O 0.250 0.000 0.875</P>
<P>O 0.750 0.000 0.125</P>
<P>O 0.750 0.000 0.375</P>
<P>O 0.750 0.000 0.625</P>
<P>O 0.750 0.000 0.875</P>
<P>O 0.000 0.250 0.125</P>
<P>O 0.000 0.250 0.375</P>
<P>O 0.000 0.250 0.625</P>
<P>O 0.000 0.250 0.875</P>
<P>O 0.000 0.750 0.125</P>
<P>O 0.000 0.750 0.375</P>
<P>O 0.000 0.750 0.625</P>
<P>O 0.000 0.750 0.875</P>
<P>O 0.250 0.500 0.125</P>
<P>O 0.250 0.500 0.375</P>
<P>O 0.250 0.500 0.625</P>
<P>O 0.250 0.500 0.875</P>
<P>O 0.750 0.500 0.125</P>
<P>O 0.750 0.500 0.375</P>
<P>O 0.750 0.500 0.625</P>
<P>O 0.750 0.500 0.875</P>
<P>O 0.500 0.250 0.125</P>
<P>O 0.500 0.250 0.375</P>
<P>O 0.500 0.250 0.625</P>
<P>O 0.500 0.250 0.875</P>
<P>O 0.500 0.750 0.125</P>
<P>O 0.500 0.750 0.375</P>
<P>O 0.500 0.750 0.625</P>
<P>O 0.500 0.750 0.875</P>
<P></P>
<P>O 0.250 0.250 0.000</P>
<P>O 0.250 0.250 0.250</P>
<P>O 0.250 0.250 0.500</P>
<P>O 0.250 0.250 0.750</P>
<P>O 0.750 0.250 0.000</P>
<P>O 0.750 0.250 0.250</P>
<P>O 0.750 0.250 0.500</P>
<P>O 0.750 0.250 0.750</P>
<P>O 0.250 0.750 0.000</P>
<P>O 0.250 0.750 0.250</P>
<P>O 0.250 0.750 0.500</P>
<P>O 0.250 0.750 0.750</P>
<P>O 0.750 0.750 0.000</P>
<P>O 0.750 0.750 0.250</P>
<P>O 0.750 0.750 0.500</P>
<P>O 0.750 0.750 0.750</P>
<P> </P>
<P>K_POINTS {automatic}</P>
<P>20 20 10 0 0 0</P></SPAN>
<P> </P>
<P>Thank you very much!</P>
<P> </P>
<P>Best regards,</P>
<P>Liwei</P>
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