Wavevector¶
The module constructs a set of wavevectors compatible with
the reciprocal space of the periodic simulation box and grouped into shells
according to their wavenumber,
. The wavevectors are of
the form
where are integers and
denote the edge length of the cuboid box.
Two modes are supported:
- a sparse sampling of thin shells according to a predefined set of wavenumbers
, allowing for a relative deviation of the wavenumber. The number of wavevectors per shell may be limited to avoid excessively large shells for large wavenumber.
- a dense grid of wavevectors from all points of the reciprocal lattice up to the maximum wavenumber given,
. The result is grouped into shells according to the wavenumbers given. In this case, shells are half-open sets,
, provided that
for all
.
The list of wavenumbers may be constructed using halmd.observables.utility.semilog_grid
,
where the smallest wavenumber is given by .
Example:
local numeric = halmd.numeric
local utility = halmd.observables.utility
local box = halmd.mdsim.box({length={5,10,20}})
local qmin = 2 * math.pi / numeric.max(box.length)
local grid = utility.semilog_grid({start=qmin, stop=5 * math.pi, decimation=10})
local wavevector = utility.wavevector({box = box, wavenumber = grid.value, tolerance=0.05, max_count=7})
-
class
halmd.observables.utility.
wavevector
(args)¶ Construct instance of wavevector module.
Parameters: - args (table) – keyword arguments
- args.box – instance of
halmd.mdsim.box
- args.wavenumber (table) – list of wavenumbers
- args.dense (boolean) – dense grid of wavevectors (default:
false
) - args.tolerance (number) – relative tolerance on wavevector magnitude
- args.max_count (integer) – maximum number of wavevectors per wavenumber shell
- args.filter (table) – filter on wavevectors (default:
{1, …, 1}
)
If
dense
istrue
, a dense grid of wavevectors is created. Otherwise, the argumentstolerance
andmax_count
are required and a sparse sampling of wavevectors is returned.The argument
filter
contains 0 or 1 for each Cartesian coordinate, 0 deletes the respective wavevector component.-
wavenumber
()¶ Returns data slot that yiels the wavenumber grid.
-
value
()¶ Returns data slot that yiels the list of wavevectors grouped by their magnitude in ascending order.
-
__eq
(other)¶ Parameters: other – instance of halmd.observables.utility.wavevector
Implements the equality operator
a = b
and returns true if the otherwavevector
instance is the same as this one.
-
halmd.observables.utility.wavevector.
add_options
(parser, defaults)¶ Add module options to command line parser:
wavenumbers
,tolerance
,max-count
.Parameters: - parser – instance of
halmd.utility.program_options.argument_parser
- defaults (dictionary) – default values for the options
- parser – instance of