[CPMD-list] About cohesive energy!

[=?gb2312?B?c2h5bWE=?=]

Dear aspi and other cpmd-user:
     Thanks for your reply!
     According to your advice, I set the same energy cutoff 30 Ry for isolate al and bulk al enrgy calculation and cancel K point shift( I just pick up it from the cpmd-test si bluk calculation and don't understand it clearly). Then the energy I get for isolate Al and bulk per atom are -49.569532 ev and -54.780587 ev respectively, so the cohesive energy of Al 5.211 ev is also far from the experiment value 3.39 ev. The two input-file follow( if you find something wrong please correct it):

for the isolate:
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
&INFO
 isolate Al atom
&END

&CPMD
 OPTIMIZE WAVEFUNCTION
 CONVERGENCE ORBITAL
 1.0D-6
 MIRROR
 LOCAL SPIN DENSITY
 MAXSTEP
 100
&END

&DFT
 FUNCTIONAL LDA
&END

&SYSTEM
 SYMMETRY
 0
 CELL
 10.0  1.0  1.0  0.0  0.0  0.0
 ANGSTROM
 MULTIPLICITY
 4
 SCALE
 CUTOFF
 30
&END

&ATOMS
*Al_GO_LDA.psp  KLEINMAN-BYLANDER
   LMAX=P
   1
   1/2  1/2  1/2
&END

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

for the Al bulk per aotm:
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
&INFO
 Bulk Al
 k-point calculation with 1 atom (primitive cell)
 with 8x8x8 MP-mesh and shift.
&END

&CPMD
  OPTIMIZE WAVEFUNCTION
  CONVERGENCE ORBITALS
   1.0D-6
  PRINT FORCES ON
  MAXSTEP
  200
  MIRROR
&END

&DFT
  FUNCTIONAL LDA
&END

&SYSTEM
  SYMMETRY
  2
  SCALE
  ANGSTROM
  CELL
  4.05 1.0  1.0  0  0  0
  CUTOFF
  30.0
  KPOINTS MONKHORST-PACK
   8 8 8
&END

&ATOMS
*Al_GO_LDA.psp  KLEINMAN-BYLANDER
   LMAX=P
   1
   0.00 0.00 0.00
&END

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

And I find if I cancle the K-point in the latter (bulk) input-file, the energy is -53.193279ev, so the cohesive energy is 3.62274 ev which approch the experiment value 3.39 ev. So why the difference is so much with no K-point? Which input-file is right, with the K-point or without K-point? If I want to get the bulk energy, should I use the K-point? Or in which case should I use the K-point?

    Lastly, the 'RAGGIO=1.6' in my input just base on my mind, because I find ' Core charge cutoff radius :   1.60000  ' in the Ti pesudopentional file, I don't know if it's suitable in the calculation! Need I specify the RAGGIO in the calculation? Which case should I do it?

Thanks and expecting your reply!
Best wishes!

                                                    shyma
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