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waves


wave

displaces the atoms along a wave. It generates sublevel with prompt "discus/wave >".

Further help topics are:

commands

Valid commands at this level are

@       ! Execute a macro file (see main help)
=       ! assigns the value to a variable (see main help)
acco    ! Sets the wave type to acoustic
amp     ! sets the amplitude in Angstroem
asym    ! Shows asymmetric unit
chem    ! Shows the atoms present in the crystal
dens    ! sets the wave type to density wave
des     ! deselects atoms
echo    ! echo a string (see main help)
eval    ! Evaluates an expression for interactive check (see main help)
exit    ! terminates 'wave'
func    ! sets the wave function
help    ! gives on line help for waves (see main help)
len     ! sets the wave length in Angstroem
long    ! sets the wave type to longitudinal
opti    ! sets the wave type to optical
osci    ! oscillation vector for transverse waves
phase   ! sets the phase of the wave at 0,0,0 in direct space
phigh   ! sets the high probability for density waves
plow    ! sets the low probability for density waves
repl    ! selects atoms to be replaced by a density wave
run     ! starts the calculation of the wave
sel     ! selects atoms to be included in the wave
shift   ! allows a constant shift to be added to the displacement
show    ! show current settings
system  ! Executes operating system command (see main help)
tran    ! sets the wave type to transverse
vect    ! sets wave vector
wait    ! Waits for user input (see main help)

acco

acco

Sets the wave type to acoustic, atoms of opposite charge are displaced in the same direction.

amp

amp <value>

sets the amplitude in Angstroem

asym

asym

Shows the content of the asymmetric unit. The names of those atoms, a number that is used as index for its scattering type, their position and temperature coefficient are listed. The number that is listed, is the number that refers to the scattering curve of that atom. It is contained in the variable m[<index>]. If a cell was read, all atoms are considered to be different, even if they are chemically identical and have the same temperature coefficient. If a whole structure was read, all atoms that are in the unit cell 0 <= xyz < 1, are chemically unique and have a different temperature coefficient are included in the asymmetric unit.

chem

chem

Displays the type of atoms present in the crystal. For each type of atom, its scattering curve number, its name and its temperature factor are listed. Warning, even, if all atoms of a particular type have been deleted, its scattering type will remain in the list. This list could therefore include more types of atoms than are actually present in the crystal.

dens

dens

Sets the type of the wave to be a density wave. All atoms selected by 'sel' or 'repl' will be modulated by the wave. The probability with which an atom is present oscillates between 'plow' and 'phigh'.

des

des { "all" | <name> | <number> } [ , { <name> | <number> } ...]
des "mic"

Deselcts choices made by ==> 'sel' or ==> 'repl'. Possible values for the parameter are mutually exclusively:

"all"     all atoms of the crystal are deselected.
"mic"     The selection of atoms that are inside a microdomain is canceled.
<name>    all the atoms called <name> of the crystal are deselected.
          This includes symmetrically not equivalent atoms.
<number>  all atoms of the crystal that are of scattering type <name>
          are deselected.

More than one atom may be deselected at once.

func

func { "box" | "sinus" | "triang" }

Sets the type of wave function used. The parameter can be any of the strings listed.

A) displacement waves:

"box"   : A box shaped wave function is used. The displacement is equal
          to amp along half the wave length and zero else.
          The displacement is amp from -1/4 to +1/4 wave length and zero
          from +1/4 to +3/4 wavelength. The point +1/4 is displaced by amp,
          the point -1/4=3/4 is not displaced.
          You can modify this range by changing the phase at the origin of
          direct space, see ==> 'phase'.
"sinus" : A sinusoidal wave function is used. The displacement is given
          by amp*SIN(arg).
"triang": A triangular displacement is applied. The displacement linearly
          increases from zero to amp and drops back to zero at the end
          of the wave. The point at 0/4 = 4/4 wave length has displacement
          zero.

The constant shift is added to these displacements.

B) replacement waves:

"box"   : A box shaped wave function is used. The occupation probability of
          the original atom, see ==> 'repl', is equal to <plow> along half
          the wave length and <phigh> else.
          The probability is <phigh> from -1/4 to +1/4 wave length and
          <plow> from +1/4 to +3/4 wavelength. The point +1/4 has the
          probability <plow> the point -1/4=3/4 has probability <phigh>.
          You can modify this range by changing the phase at the origin of
          direct space, see ==> 'phase'.
"sinus" : A sinusoidal wave function is used. The occupation probability
          is given by
          amp * SIN(arg) + amp0, where
          amp = 0.5*( phigh-plow)
          amp0= 0.5*( phigh+plow)
          This will give a sinusoidal wave with minimum at <plow> and
          maximum value at <phigh>.
"triang": A triangular occupation probability is applied. The occupation
          probability linearly increases from <plow> to <phigh> and drops
          back to zero at the end of the wave.
          The point at 0/4 = 4/4 wave length has the occupation
          probability of <plow>.

len

len <value>

sets the wave length in Angstroem

long

long

sets the wave type to longitudinal

opti

opti

sets the wave type to optical, atoms of opposite charge are displaced in opposite directions

osci

osci <x,y,z>

sets the direction of the oscillation vector for transverse waves

phase

phase { <value> | "random" }

sets the phase of the wave at 0,0,0 in direct space in degrees. The initial phase is zero. With phase = 0, a sine wave results, with phase = 90 a cosine wave. The phase type "random" causes a random phase for each microdomain.

phigh

phigh <value>

sets the upper probability limit, with which an atom is retained by a density wave. The maximum occupancy of the atom reaches <value>.

plow

plow <value>

sets the lower probability limit, with which an atom is retained by a density wave. The minimum occupancy of the atom reaches <value>.

repl

repl { "all" | <name> | <number> } , { <name> | <number> }
repl "mic",{ "all" | "eve" | "non" | <number> }

This command executes two different functions. It serves to select those atoms that will be replaced by a density function and secondly it can set the microdomain status.

First function: Defines which atoms are replaced by a density waves. Possible values for the first mandatory parameter are mutually exclusively:

"all"     all atoms of the crystal are replaced by the atom defined
          by the second parameter.
<name>    all the atoms called <name> of the crystal are replaced by
          the atom defined by the second parameter. This includes
          symmetrically not equivalent atoms.
<number>  all atoms of the crystal that are of scattering type <name>
          are replaced by the atom defined by the second parameter.

The second parameter defines the atom, the original is replaced by. If a name is given, it need not to be present in the original crystal. A new scattering type is automatically added to the table. If a number is given, to which no corresponding atom exists, an error message is displayed.

Second function: Defines how atoms inside any microdomains are to be treated. The second parameter serves to distinguish different possible values of the status.

"mic"     selects whether atoms that are inside a microdomain are to be
          replaced by the wave or not.
          The kind of atoms to be included are to be chosen by an
          additional 'sel' command.
          Second parameter:
          "all"    atoms inside any microdomain are replaced , all atoms
                   outside all microdomains are not included.
          "eve"    Disregard microdomain status of an atom. Atoms in the
                   host structure and inside any microdomain are included
                   alike.
          "none"   Only atoms outside all microdomains are replaced.
          <number> Only atoms inside microdomain type <number> are replaced.

run

run

Starts the calculation of the wave

sel

sel { "all" | <name> | <number> } [ , { <name> | <number> } ...]
sel "mic",{ "all" | "eve" | "non" | <number> }

This command executes two different functions. It serves to select those atoms that will be modified by a wave function and secondly it can set the microdomain status.

First function:

Defines which atoms are included in a wave. Possible values for the first mandatory parameter are mutually exclusively:

"all"     all atoms of the crystal are included.
<name>    all the atoms called <name> of the crystal are included.
          This includes symmetrically not equivalent atoms.
<number>  all atoms of the crystal that are of scattering type <number>
          are included.

More than one atom may be selected at once.

Second function:

Defines how atoms inside any microdomains are to be treated. The second parameter serves to distinguish different possible values of the status.

"mic"     selects whether atoms that are inside a microdomain are to be
          modified by the wave or not.
          The kind of atoms to be included are to be chosen by an
          additional 'sel' command.
          Second parameter:
          "all"    atoms inside any microdomain are selected, all atoms
                   outside all microdomains are not included.
          "eve"    Disregard microdomain status of an atom. Atoms in the
                   host structure and inside any microdomain are included
                   alike.
          "none"   Only atoms outside all microdomains are selected.
          <number> Only atoms inside microdomain type <number> are selected.

The selection made stay valid until explicitely deselected!

shift

shift <amount>

A constant shift <amount> is added to the displacement of the atoms

show

show

shows the current settings for the wave.

tran

tran

sets the wave type to transverse

vect

vect <x,y,z>

sets the direction of the wave vector in units of the lattice constants. The wave length has to be set with ==> "len".


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