不好意思，又要麻烦您了，前几天在学习对体系进行full-relax,用vc-relax进行计算，在优化后它会自动进行一次自洽计算，但是奇怪的是，两次的原子位置却有点不大一样，我怎么看也不明白为什么，所以要麻烦您了，我给您把数据贴出来：
End of BFGS Geometry Optimization
Final enthalpy = -167.8961699933 Ry
Begin final coordinates
new unit-cell volume = 409.58929 a.u.^3 ( 60.69487 Ang^3 )
ATOMIC_POSITIONS (crystal)
Cr 0.000000000 0.000000000 -0.000000000
Cr 0.500000000 0.500000000 0.500000000
O 0.304047718 0.304047718 -0.000000000
O 0.695952282 0.695952282 0.000000000
O 0.804047718 0.195952282 0.500000000
O 0.195952282 0.804047718 0.500000000
End final coordinates
A final scf calculation at the relaxed structure.
The G-vectors are recalculated for the final unit cell
Results may differ from those at the preceding step.
Parallelization info
--------------------
sticks: dense smooth PW G-vecs: dense smooth PW
Min 858 858 234 35945 35945 5075
Max 859 859 236 35946 35946 5076
Sum 6869 6869 1877 287563 287563 40605
bravais-lattice index = 0
lattice parameter (alat) = 8.3503 a.u.
unit-cell volume = 409.5893 (a.u.)^3
number of atoms/cell = 6
number of atomic types = 2
number of electrons = 36.00
number of Kohn-Sham states= 22
kinetic-energy cutoff = 300.0000 Ry
charge density cutoff = 1200.0000 Ry
convergence threshold = 3.8E-12
mixing beta = 0.7000
number of iterations used = 8 plain mixing
Exchange-correlation = SLA-PZ-NOGX-NOGC ( 1 1 0 0 0)
EXX-fraction = 0.00
PseudoPot. # 1 for Cr read from file:
/home/liushichen/tools/codes/espresso-4.3.2/pseudo/Cr.pz-hgh.UPF
MD5 check sum: 1ecfd84ed12b05c881064968d61b62c6
Pseudo is Norm-conserving, Zval = 6.0
Generated in analytical, separable form
Using radial grid of 1183 points, 6 beta functions with:
l(1) = 0
l(2) = 0
l(3) = 0
l(4) = 1
l(5) = 1
l(6) = 2
PseudoPot. # 2 for O read from file:
/home/liushichen/tools/codes/espresso-4.3.2/pseudo/O.pz-hgh.UPF
MD5 check sum: 9c3213c38e11527cd347dae851a6ebc4
Pseudo is Norm-conserving, Zval = 6.0
Generated in analytical, separable form
Using radial grid of 1095 points, 1 beta functions with:
l(1) = 0
atomic species valence mass pseudopotential
Cr 6.00 52.00000 Cr( 1.00)
O 6.00 16.00000 O( 1.00)
Starting magnetic structure
atomic species magnetization
Cr 0.500
O 0.000
LDA+U calculation, Hubbard_lmax = 2
atomic species L Hubbard U Hubbard alpha
Cr 2 0.220496 0.000000
16 Sym.Ops. (with inversion)
Cartesian axes
site n. atom positions (alat units)
1 Cr tau( 1) = ( 0.0000000 0.0000000 -0.0000000 )
2 Cr tau( 2) = ( 0.5080391 0.5080391 0.3406890 )
3 O tau( 3) = ( 0.3089362 0.3089362 -0.0000000 )
4 O tau( 4) = ( 0.7071419 0.7071419 0.0000000 )
5 O tau( 5) = ( 0.8169753 0.1991028 0.3406890 )
6 O tau( 6) = ( 0.1991028 0.8169753 0.3406890 )
这是在vc-relax的out文件里的，上面那个的意思应该就是优化好了，然后就直接自动进行了一次自洽，我认为你应该就用优化好的结构参数把，为什么原子位置却有点出入呢？谢谢!
送红花一朵 
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