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This keyword allows you to specify options for Periodic Boundary Conditions jobs. Note PBC is turned on simply by including translation vectors in the input structure, and this keyword is used only to control how PBC calculations are performed. If you do not need any of these options, you do not have to include the keyword to perform a PBC calculation.


Do just the Γ point (k=0) rather than full k-integration.


Do approximately N k-points.


Go out N Bohr in each direction in setting up image cells.


Include at least N cells.


Include at most N cells in any part of the calculation.


Include at least N cells in DFT XC quadrature. NCellXC is a synonym for this option.


Include at least N cells in exact exchange. By default, if exact exchange is included, then this is twice the number of cells used for overlap-related quantities and XC quadrature.

HF and DFT analytic energy and optimizations, and numerical frequencies (no IR intensities). Not valid with SCRF or Charge. For periodic systems of any reasonable size, acceptable performance may only be feasible by using a pure DFT functional in combination with density fitting.

Periodic systems are specified with a normal molecule specification for the unit cell. The only additional required input are one, two or three translation vectors appended to the molecule specification (with no intervening blank line), indicating the replication direction(s). For example, the following input specifies a one-dimensional PBC single point energy calculation for neoprene:

# PBEPBE/6-31g(d,p)/Auto SCF=Tight 

neoprene, -CH2-CH=C(Cl)-CH2- optimized geometry

0 1

The final line specifies the translation vector. Note that it specifies TV as the atom symbol.

The following molecule specification could be used for a two-dimensional PBC calculation on a graphite sheet:

0 1
C                  0.000000    0.000000    0.000000
C                  0.000000    1.429118    0.000000
TV                 2.475315    0.000000    0.000000
TV                -1.219952    2.133447    0.000000

Here is the molecule specification that could be used for a three-dimensional PBC calculation on gallium arsenide:

0 1
 Ga                 0.000000    0.000000    0.000000
 Ga                 0.000000    2.825000    2.825000
 Ga                 2.825000    0.000000    2.825000
 Ga                 2.825000    2.825000    0.000000
 As                 1.412500    1.412500    1.412500
 As                 1.412500    4.237500    4.237500
 As                 4.237500    1.412500    4.237500
 As                 4.237500    4.237500    1.412500
 TV                 5.650000    0.000000    0.000000
 TV                 0.000000    5.650000    0.000000
 TV                 0.000000    0.000000    5.650000

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