displaces the atoms along a wave. It generates sublevel with prompt "discus/wave >".
Further help topics are:
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)
Sets the wave type to acoustic, atoms of opposite charge are displaced in the same direction.
sets the amplitude in Angstroem
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.
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.
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'.
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.
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>.
sets the wave length in Angstroem
sets the wave type to longitudinal
sets the wave type to optical, atoms of opposite charge are displaced in opposite directions
sets the direction of the oscillation vector for transverse waves
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.
sets the upper probability limit, with which an atom is retained by a density wave. The maximum occupancy of the atom reaches <value>.
sets the lower probability limit, with which an atom is retained by a density wave. The minimum occupancy of the atom reaches <value>.
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.
Starts the calculation of the wave
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!
A constant shift <amount> is added to the displacement of the atoms
shows the current settings for the wave.
sets the wave type to transverse
sets the direction of the wave vector in units of the lattice constants. The wave length has to be set with ==> "len".