Rdf2

Namespaces
namespace	rdf2
	Defines RDF-specific functions.

Functions
int	rdf2::rdf2Danalysis_AA (std::string path, std::vector< double > *rdfValues, molSys::PointCloud< molSys::Point< double >, double > *yCloud, double cutoff, double binwidth, int firstFrame, int finalFrame)
std::vector< int >	rdf2::sampleRDF_AA (molSys::PointCloud< molSys::Point< double >, double > *yCloud, double cutoff, double binwidth, int nbin)
	Samples the RDF histogram at every step.
int	rdf2::normalizeRDF (int nopA, std::vector< double > *rdfValues, std::vector< int > histogram, double binwidth, int nbin, std::vector< double > volumeLengths, int nIter)
	Normalize the histogram.
std::vector< double >	rdf2::getSystemLengths (molSys::PointCloud< molSys::Point< double >, double > *yCloud)
	Gets the lengths of the volume slice of the quasi-two-dimensional system.
double	rdf2::getPlaneArea (std::vector< double > volumeLengths)
	Gets the plane area from the volume lengths vector.

Detailed Description

Function Documentation

getPlaneArea()

double rdf2::getPlaneArea

(

std::vector< double >

volumeLengths

)

Gets the plane area from the volume lengths vector.

Calculates the plane area from the volume lengths. This is the product of the two largest dimensions of the quasi-two-dimensional system.

Parameters

[in]

volumeLengths

A vector of the lengths of the volume slice or simulation box

Returns

The plane area of the two significant dimensions

Definition at line 264 of file rdf2d.cpp.

Code

                                                         {
  //
  // Sort the vector in descending order
  std::sort(volumeLengths.begin(), volumeLengths.end());
  std::reverse(volumeLengths.begin(), volumeLengths.end());
 
  return volumeLengths[0] * volumeLengths[1];
 
} // end of function

getSystemLengths()

std::vector< double > rdf2::getSystemLengths

(

molSys::PointCloud< molSys::Point< double >, double > *

yCloud

)

Gets the lengths of the volume slice of the quasi-two-dimensional system.

Calculates the lengths of the quasi-two-dimensional system. The smallest length is the 'height'.

Parameters

[in]

yCloud

The molSys::PointCloud struct for the system.

Returns

The length (i.e. the 'height') of the smallest dimension of quasi-two-dimensional system.

Definition at line 212 of file rdf2d.cpp.

Code

                                                           {
  //
  std::vector<double> lengths; // Volume lengths
  std::vector<double>
      rMax; // Max of the coordinates {0 is for x, 1 is for y and 2 is for z}
  std::vector<double>
      rMin; // Min of the coordinates {0 is for x, 1 is for y and 2 is for z}
  std::vector<double> r_iatom; // Current point coordinates
  int dim = 3;
 
  // Init
  r_iatom.push_back(yCloud->pts[0].x);
  r_iatom.push_back(yCloud->pts[0].y);
  r_iatom.push_back(yCloud->pts[0].z);
  rMin = r_iatom;
  rMax = r_iatom;
 
  // Loop through the entire PointCloud
  for (int iatom = 1; iatom < yCloud->nop; iatom++) {
    r_iatom[0] = yCloud->pts[iatom].x; // x coordinate of iatom
    r_iatom[1] = yCloud->pts[iatom].y; // y coordinate of iatom
    r_iatom[2] = yCloud->pts[iatom].z; // z coordinate of iatom
    // Loop through every dimension
    for (int k = 0; k < dim; k++) {
      // Update rMin
      if (r_iatom[k] < rMin[k]) {
        rMin[k] = r_iatom[k];
      } // end of rMin update
      // Update rMax
      if (r_iatom[k] > rMax[k]) {
        rMax[k] = r_iatom[k];
      } // end of rMax update
    }   // end of looping through every dimension
  }     // end of loop through all the atoms
 
  // Get the lengths
  for (int k = 0; k < dim; k++) {
    lengths.push_back(rMax[k] - rMin[k]);
  } // end of updating lengths
 
  return lengths;
} // end of function

normalizeRDF()

int rdf2::normalizeRDF	(	int	nopA,
		std::vector< double > *	rdfValues,
		std::vector< int >	histogram,
		double	binwidth,
		int	nbin,
		std::vector< double >	volumeLengths,
		int	nIter
	)

Normalize the histogram.

Normalizes the histogram and adds it to the RDF. The normalization requires the plane area and height.

Parameters

[in]	nopA	The number of particles of type A.
[in]	rdfValues	Radial distribution function values for all the frames, in the form of a vector.
[in]	histogram	The histogram for the current frame.
[in]	binwidth	The width of each bin for the RDF histogram.
[in]	nbin	The number of bins for the RDF.
[in]	volumeLengths	The confining dimensions of the quasi-two-dimensional system, which may be the slice dimensions or the dimensions of the box.
[in]	nIter	The number of iterations for which the coordinates will be binned. This is basically equivalent to the number of frames over which the RDF will be calculated.

Definition at line 162 of file rdf2d.cpp.

Code

                                                                   {
  //
  auto height = *std::min_element(
      volumeLengths.begin(),
      volumeLengths.end()); // The height or the smallest dimension
  // double planeArea = rdf2::getPlaneArea(
  //     volumeLengths);  // The area of the quasi-two-dimensional water
  double r;         // Distance for the current bin
  double factor;    // Factor for accounting for the two-dimensional slab
  double binVolume; // Volume of the current bin
  double volumeDensity =
      nopA / (volumeLengths[0] * volumeLengths[1] * volumeLengths[2]);
 
  // Loop through every bin
  for (int ibin = 0; ibin < nbin; ibin++) {
    //
    r = binwidth * (ibin + 0.5);
    // ----------------------
    // Factor calculation
    factor = 1;
    if (r > height) {
      // FACTOR = HEIGHT/(2*R)
      factor = height / (2 * r);
    } // r>height
    else {
      // FACTOR = 1 - R/(2*HEIGHT)
      factor = 1 - r / (2 * height);
    } // r<=height
    // ----------------------
    // binVolume = 4.0*PI*(DELTA_R**3)*((I_BIN+1)**3-I_BIN**3)/3.0
    binVolume = 4 * gen::pi * pow(binwidth, 3.0) *
                (pow(ibin + 1, 3.0) - pow(ibin, 3.0)) / 3.0;
    // Update the RDF
    (*rdfValues)[ibin] +=
        histogram[ibin] / (nIter * binVolume * nopA * volumeDensity * factor);
  } // end of loop through every bin
 
  return 0;
 
} // end of function

rdf2Danalysis_AA()

int rdf2::rdf2Danalysis_AA	(	std::string	path,
		std::vector< double > *	rdfValues,
		molSys::PointCloud< molSys::Point< double >, double > *	yCloud,
		double	cutoff,
		double	binwidth,
		int	firstFrame,
		int	finalFrame
	)

Main function for calculating the RDF for the same type of particle: calls other functions for initializing, sampling and normalizing the RDF

Calculates the in-plane RDF for quasi-two-dimensional water, when both the atoms are of the same type. The input PointCloud only has particles of type A in it. This is registered as a Lua function and is accessible to the user. Internally, this function calls the following functions:

• rdf2::getSystemLengths (Gets the dimensions of the quasi-two-dimensional system).
• ring::rdf2::sampleRDF_AA (Samples the current frame, binning the coordinates).
• ring::rdf2::normalizeRDF (Normalizes the RDF).
• ring::sout::printRDF (Writes out the RDF to the desired output directory, in the form of an ASCII file)

  Parameters

  [in]	path	The file path of the output directory to which output files will be written.
  [in]	rdfValues	Vector containing the RDF values.
  [in]	yCloud	The input PointCloud.
  [in]	cutoff	Cutoff for the RDF. This should not be greater than half the box length.
  [in]	binwidth	Width of the bin for histogramming.
  [in]	firstFrame	The first frame for RDF binning.
  [in]	finalFrame	The final frame for RDF binning.

Definition at line 45 of file rdf2d.cpp.

Code

                                                     {
  //
  int nopA = yCloud->nop; // Number of particles of type A in the current frame.
  int currentFrame = yCloud->currentFrame; // The current frame
  int nbin;                                // Number of bins
  std::vector<double> volumeLengths;       // Lengths of the volume of the
                                           // quasi-two-dimensional system
  std::vector<int> histogram; // Histogram for the RDF, at every step
  int nIter = finalFrame - firstFrame + 1; // Number of iterations
  // ----------------------------------------------
  // INITIALIZATION
  if (currentFrame == firstFrame) {
    // -----------------
    // Checks and balances?
    // -----------------
    nbin = 1 + int(cutoff / binwidth); // Number of bins
    (*rdfValues).resize(nbin);         // RDF initialized to 0
  }                                    // end of initialization
  // ----------------------------------------------
  // SAMPLING
  // Get the volume lengths of the quasi-two-dimensional system
  volumeLengths = rdf2::getSystemLengths(yCloud);
  // Update cutoff if required? later
  nbin = int(cutoff / binwidth); // Number of bins
  // Sample for the current frame!!
  histogram = rdf2::sampleRDF_AA(yCloud, cutoff, binwidth, nbin);
  // ----------------------------------------------
  // NORMALIZATION
  rdf2::normalizeRDF(nopA, rdfValues, histogram, binwidth, nbin, volumeLengths,
                     nIter);
  // ----------------------------------------------
  // PRINT OUT
  if (currentFrame == finalFrame) {
    // Create folder if required
    sout::makePath(path);
    std::string outputDirName = path + "topoMonolayer";
    sout::makePath(outputDirName);
    //
    std::string fileName = path + "topoMonolayer/rdf.dat";
    //
    // Comment line
    std::ofstream outputFile; // For the output file
    outputFile.open(fileName, std::ios_base::app | std::ios_base::out);
    outputFile << "# r  g(r)\n";
    outputFile.close();
    //
    //
    sout::printRDF(fileName, rdfValues, binwidth, nbin);
  } // end of print out
  // ----------------------------------------------
 
  return 0;
} // end of function

sampleRDF_AA()

std::vector< int > rdf2::sampleRDF_AA	(	molSys::PointCloud< molSys::Point< double >, double > *	yCloud,
		double	cutoff,
		double	binwidth,
		int	nbin
	)

Samples the RDF histogram at every step.

Samples the RDF for a particular frame The input PointCloud only has particles of type A in it.

• gen::periodicDist (Periodic distance between a pair of atoms).

  Parameters

  [in]	yCloud	The input PointCloud.
  [in]	cutoff	Cutoff for the RDF calculation, which should be less than or equal to half the box length.
  [in]	binwidth	Width of the bin.
  [in]	nbin	Number of bins.

  Returns

  RDF histogram for the current frame.

Definition at line 115 of file rdf2d.cpp.

Code

                                                             {
  //
  std::vector<int> histogram; // Histogram for the RDF
  double r_ij;                // Unwrapped distance between iatom and jatom
  int ibin; // Index of the bin in which the distance r_ij falls
 
  // Init the histogram to 0
  histogram.resize(nbin);
 
  // Loop through pairs of atoms
  for (int iatom = 0; iatom < yCloud->nop - 1; iatom++) {
    //
    // Loop through the next atom in the atom pair
    for (int jatom = iatom + 1; jatom < yCloud->nop; jatom++) {
      // Calculate the distance between iatom and jatom
      r_ij = gen::periodicDist(yCloud, iatom, jatom);
      // Check if the distance is within the cutoff. Update the histogram if
      // r_ij is within the cutoff
      if (r_ij <= cutoff) {
        ibin = int(r_ij / binwidth); // Bin in which r_ij falls
        histogram[ibin] += 2;        // Update for iatom and jatom both
      }                              // end of histogram update
    }                                // end of loop through jatom
  }                                  // end of loop through iatom
 
  // Return the histogram
  return histogram;
 
} // end of function