REFERENCE · R2

Card reference

Syntax and options for the pw.x cards: ATOMIC_*, K_POINTS, CELL_PARAMETERS and HUBBARD.

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Syntax for the card blocks that follow the namelists in a pw.x input. Namelist variables are in R1.

Cards at a glance

Card Required Options Description
ATOMIC_SPECIES yes none Label, mass, UPF filename
ATOMIC_POSITIONS yes alat / bohr / angstrom / crystal / crystal_sg Optional trailing if_pos flags
K_POINTS yes automatic / gamma / tpiba / crystal / tpiba_b / crystal_b / tpiba_c / crystal_c The _b variants are for band paths
CELL_PARAMETERS with ibrav=0 alat / bohr / angstrom 3×3 matrix
HUBBARD for DFT+U atomic / ortho-atomic / norm-atomic / wf / pseudo v7.1+ syntax
OCCUPATIONS with occupations='from_input' none Per-band occupations
CONSTRAINTS constrained relax/MD none Bond and angle constraints
ATOMIC_VELOCITIES MD restart a.u.
ATOMIC_FORCES applied forces none
ADDITIONAL_K_POINTS special none
SOLVENTS RISM none

ATOMIC_SPECIES

ATOMIC_SPECIES
  Fe1  55.845  Fe.pbe-spn-kjpaw_psl.1.0.0.UPF
  Fe2  55.845  Fe.pbe-spn-kjpaw_psl.1.0.0.UPF   ! same file, second label: for AFM
  O    15.999  O.pbe-n-kjpaw_psl.1.0.0.UPF

The number of lines must equal ntyp. The same pseudopotential may be registered under several labels; antiferromagnetic order (Chapter 12) and per-atom U (Chapter 13) rely on exactly this. The mass matters physically only in MD and phonons.

ATOMIC_POSITIONS

ATOMIC_POSITIONS (crystal)
  Fe  0.000  0.000  0.000   0 0 0    ! if_pos: fully fixed
  Fe  0.500  0.500  0.250   0 0 1    ! free along z only
  O   0.500  0.000  0.375              ! omitted = 1 1 1 (fully free)
Option Meaning
alat Cartesian, in units of celldm(1)
bohr / angstrom Absolute Cartesian
crystal Fractional in the cell basis (safest in practice)
crystal_sg Space-group coordinates (with space_group)

The if_pos triplet (0/1) zeroes the force components in optimization and MD, freezing motion along those directions.

K_POINTS

K_POINTS (automatic)      ! Monkhorst-Pack grid
  8 8 8  0 0 0            ! nk1 nk2 nk3  s1 s2 s3 (shifts 0/1)

K_POINTS gamma            ! Γ only (isolated molecules); real wavefunctions

K_POINTS (tpiba_b)        ! band path, Cartesian in 2π/a
6
  0.500 0.500 0.500  30   ! point + divisions to the next point
  ...
  0.000 0.000 0.000   0   ! last point gets 0

K_POINTS (crystal)        ! explicit list with weights
  • The difference between tpiba_b (Cartesian, 2π/a) and crystal_b (fractional, reciprocal basis) is explained in Chapter 10. When in doubt, tpiba_b is safe.
  • An nscf feeding the tetrahedron method must use an unshifted, Γ-centered automatic grid.

CELL_PARAMETERS

CELL_PARAMETERS (angstrom)
  -2.715   0.000   2.715
   0.000   2.715   2.715
  -2.715   2.715   0.000

Three cell vectors as rows, used with ibrav=0. With the alat option the matrix is scaled by celldm(1) (or A), which is convenient for volume scans and vc-relax restarts.

HUBBARD (v7.1+)

HUBBARD (ortho-atomic)
U Fe1-3d 4.6
U Fe2-3d 4.6
V Fe1-3d O-2p  1 3  0.8    ! DFT+U+V; site indices follow ATOMIC_POSITIONS order

Grammar: HUBBARD (<projector>), then lines of <parameter> <label>-<manifold> <value(eV)>.

Field Options
Projector atomic / ortho-atomic (recommended) / norm-atomic / wf / pseudo
Parameter U, J0, J, B, E2, E3, V, alpha
Manifold 3d, 2p, 4f, ... (up to 3 channels per type)

The old syntax (lda_plus_u, Hubbard_U(i)) is retired. Details in Chapter 13 and Doc/Hubbard_input.pdf.

OCCUPATIONS

With occupations='from_input', list the occupation of every band; in spin-polarized runs the up block comes first, then the down block. Rarely needed outside constrained or excited-state tricks.

CONSTRAINTS

CONSTRAINTS
1
'distance' 1 2 2.40      ! constrain the distance of atoms 1-2 to 2.40 bohr

For constrained optimization and MD. First line is the number of constraints, then one per line ('distance', 'planar_angle', 'torsional_angle', ...).

The neb.x input layout (for reference)

neb.x uses a block structure rather than cards:

BEGIN
BEGIN_PATH_INPUT
&PATH
  string_method = 'neb'
  num_of_images = 7
  nstep_path    = 100
  opt_scheme    = 'broyden'
  path_thr      = 0.05
/
END_PATH_INPUT
BEGIN_ENGINE_INPUT
&CONTROL
 ... (identical to a pw.x input)
/
BEGIN_POSITIONS
FIRST_IMAGE
ATOMIC_POSITIONS (crystal)
 ...
LAST_IMAGE
ATOMIC_POSITIONS (crystal)
 ...
END_POSITIONS
END_ENGINE_INPUT
END

Background in Chapter 17.