Synopsis

This analyzer calculates a Van Hove function S(q,t) for a specified set of wavevectors. The van Hove function for each wavevector q is defined as an autocorrelation function for a Fourier amplitude that is defined using a mode vector, by assigning a weight coefficient to each atom type, as in the StructurFactor diagnostic. The array of atomTypeCoeffs parameters used here is equivalent to the "mode" arrays defined in StructureFactor class. See the class definition See the DdMd::VanHove class documentation for a precise definition of S(q,t).

See also: DdMd::VanHove; Util::IntVector

Parameters

The parameter file format is:

VanHove{ 
   interval           int
   outputFileName     string
   atomTypeCoeffs     Array<double> [nAtomType]
   nBuffer            int
   nWave              int
   waveIntVectors     Array<IntVector> [nWave]
}

in which

interval	number of steps between data samples
outputFileName	name of output file
atomTypeCoeffs	Each row is a vector of dimension nAtomType, which specifies a set of weight factors for different atom types in the calcultation of Fourier amplitudes.
nBuffer	number of time separation values.
nWave	number of reciprocal lattice wavevectors.
waves	array of reciprocal lattice vectors, each specified on a separate line by 3 integer indices (Miller indices)

Example

Consider a system with nAtomType = 2, with two monomer types 0 and 1. The correlation function for the composition, defined as a difference between the A and B monomer concentrations, can be calculated using the mode vector (1,-1). A parameter file input for calculating S(q,t) for the composition mode for 5 wavevectors along the x axis in a cubic or orthorhombic unit cell might look like this:

VanHove{
   interval                      1000
   outputFileName             VanHove
   nBuffer                        100
   atomTypeCoeffs            1     -1
   nWave                            5
   waveIntVectors     8      0      0
                      9      0      0 
                     10      0      0 
                     11      0      0 
                     12      0      0 
}

Output Files

At the end of a simulation, all of the structure factors are output in a file {outputFileName}.dat. Results for different wavevectors are listed consecutively in blocks. Each block begins with the integer indices (Miller indices) for the associated wavevector.