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Plotting electronic orbitals using Mathematica

2013-09-27 by . 7 comments

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As a chemist it is often useful to plot electronic orbitals.  These are used to describe the wave function of electrons in atoms or molecules.  Typically, these are output from electronic structure software in the form of a cube file, first developed by Gaussian.  These files contain volumetric data for a given orbital on a three-dimensional grid.

There exist many applications to visualize cube files, such as VMD or GaussView, but I wanted to take advantage of Mathematica‘s  capability to easily combine graphics, as well as the ability to automate the process in order to efficiently create frames for a movie.

First off, we need a function to extract the data from the cube file.  In the process, we will create the text for an XYZ file, a format also developed by Gaussian.  The function OutForm is used here to mimic the printf function found in other programming languages.

OutForm[num_?NumericQ, width_Integer, ndig_Integer, 
   OptionsPattern[]] :=
  Module[{mant, exp, val},
   {mant, exp} = MantissaExponent[num];
   mant = ToString[NumberForm[mant, {ndig, ndig}]];
   exp = If[Sign[exp] == -1, "-", "+"] <> IntegerString[exp, 10, 2];
   val = mant <> "E" <> exp;
   StringJoin@PadLeft[Characters[val], width, " "]
   ];

ReadCube[cubeFileName_?StringQ] := Module[ {moltxt, nAtoms, lowerCorner, nx, ny, nz, xstep, ystep, zstep, atoms, desc1, desc2, xyzText, cubeDat, xgrid, ygrid, zgrid, dummy1, dummy2, atomicNumber, atomx, atomy, atomz, tmpString, headerTxt,bohr2angstrom}, bohr2angstrom = 0.529177249; moltxt = OpenRead[cubeFileName]; desc1 = Read[moltxt, String]; desc2 = Read[moltxt, String]; lowerCorner = {0, 0, 0}; {nAtoms, lowerCorner[[1]], lowerCorner[[2]], lowerCorner[[3]]} = Read[moltxt, String] // ImportString[#, "Table"][[1]] &; xyzText = ToString[nAtoms] <> "\n"; xyzText = xyzText <> desc1 <> desc2 <> "\n"; {nx, xstep, dummy1, dummy2} = Read[moltxt, String] // ImportString[#, "Table"][[1]] &; {ny, dummy1, ystep, dummy2} = Read[moltxt, String] // ImportString[#, "Table"][[1]] &; {nz, dummy1, dummy2, zstep} = Read[moltxt, String] // ImportString[#, "Table"][[1]] &; Do[ {atomicNumber, dummy1, atomx, atomy, atomz} = Read[moltxt, String] // ImportString[#, "Table"][[1]] &; xyzText = If[Sign[lowerCorner[[1]]] == 1, xyzText <> ElementData[atomicNumber, "Abbreviation"] <> OutForm[atomx, 17, 7] <> OutForm[atomy, 17, 7] <> OutForm[atomz, 17, 7] <> "\n", xyzText <> ElementData[atomicNumber, "Abbreviation"] <> OutForm[bohr2angstrom atomx, 17, 7] <> OutForm[bohr2angstrom atomy, 17, 7] <> OutForm[bohr2angstrom atomz, 17, 7] <> "\n"]; , {nAtoms}]; cubeDat = Partition[Partition[ReadList[moltxt, Number, nx ny nz], nz], ny]; Close[moltxt]; moltxt = OpenRead[cubeFileName]; headerTxt = Read[moltxt, Table[String, {2 + 4 + nAtoms}]]; Close[moltxt]; headerTxt = StringJoin@Riffle[headerTxt, "\n"]; xgrid = Range[lowerCorner[[1]], lowerCorner[[1]] + xstep (nx - 1), xstep]; ygrid = Range[lowerCorner[[2]], lowerCorner[[2]] + ystep (ny - 1), ystep]; zgrid = Range[lowerCorner[[3]], lowerCorner[[3]] + zstep (nz - 1), zstep]; {cubeDat, xgrid, ygrid, zgrid, xyzText, headerTxt} ];

If you need to create a cube file, then the following function can be used:
WriteCube[cubeFileName_?StringQ, headerTxt_?StringQ, cubeData_] := 
 Module[{stream}, 
  stream = OpenWrite[cubeFileName, FormatType -> FortranForm];
  WriteString[stream, headerTxt, "\n"];
  Map[WriteString[stream, ##, "\n"] & @@ 
     Riffle[ScientificForm[#, {3, 4}, 
         NumberFormat -> (Row[{#1, "E", If[#3 == "", "+00", #3], 
              "\t"}] &), NumberPadding -> {"", "0"}, 
         NumberSigns -> {"-", " "}] & /@ #, "\n", {7, -1, 7}] &, 
   cubeData, {2}];
  Close[stream];]
Next we need the function to plot the orbital,
CubePlot[{cub_, xg_, yg_, zg_, xyz_}, plotopts : OptionsPattern[]] := 
   Module[{xyzplot, bohr2picometer, datarange3D, pr},
    bohr2picometer = 52.9177249;
    datarange3D = 
      bohr2picometer {{xg[[1]], xg[[-1]]}, {yg[[1]], 
         yg[[-1]]}, {zg[[1]], zg[[-1]]}};
    xyzplot = ImportString[xyz, "XYZ"];
    Show[xyzplot, 
     ListContourPlot3D[Transpose[cub, {3, 2, 1}], 
       Evaluate[FilterRules[{plotopts}, Options[ListContourPlot3D]]], 
       Contours -> {-.02, .02}, ContourStyle -> {Blue, Red}, 
       DataRange -> datarange3D, MeshStyle -> Gray, 
       Lighting -> {{"Ambient", White}}], 
       Evaluate[
        FilterRules[{plotopts}, {ViewPoint, ViewVertical, ImageSize}]]]
    ];    
Let’s look at an example. Download the file cys-MO35.cube and place it in your home directory (or anywhere in your $Path). Then, read in the cube file with:
{cubedata,xg,yg,zg,xyz,header}= ReadCube["cys-MO35.cube"];
and plot it via
CubePlot[{cubedata, xg, yg, zg, xyz}]
pizCq

When I want to create a movie file, I want all the images to have exactly the same ViewAngle, ViewPoint, and ViewCenter.  When you give these options to CubePlot, it feeds them directly to the Show function

vp = {ViewCenter -> {0.5, 0.5, 0.5}, 
   ViewPoint -> {1.072, 0.665, -3.13}, 
   ViewVertical -> {0.443, 0.2477, 1.527}};

CubePlot[{cubedata, xg, yg, zg, xyz}, vp]

Q1mjs

Finally, you can also give any options that normally go to ListContourPlot3D

CubePlot[{cubedata, xg, yg, zg, xyz}, vp, 
 ContourStyle -> {Texture[ExampleData[{"ColorTexture", "Vavona"}]], 
   Texture[ExampleData[{"ColorTexture", "Amboyna"}]]}, 
 Contours -> {-.015, .015}] 
fLyJ7

Many thanks to Daniel Healion for the ReadCube and WriteCube functions.

Filed under chemistry graphics

7 Comments

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  • rcollyer says:

    I never used Guassian, but Wien2k was my mainstay. I never considered posting the stuff I used for generating plots from it, though. Nice.

  • Jason B says:

    To anyone trying to work the example, for now you have to extract the archive yoursef, as Mathematica won’t extract it properly.

  • I tried to import the “cys-MO35cube” file extracted from the archive and placed in $UserBaseDirectory using the {cubedata,xg,yg,zg,xyz,header}= ReadCube["cys-MO35.cube"]; command and {cubedata,xg,yg,zg,xyz,header}= ReadCube["cys-MO35cube"]; command but it fails. I am using MMa 8.0.4 under Win 7 x64. How it is supposed to work?

  • Jason B says:

    Alexey, my apologies. The blog here keeps renaming my gzip archive, which then somehow renames the file inside the archive. So basically the extracted file doesn’t have the right filename. I’m very unfamiliar with the gzip format. I first tried to just upload the cube file in its uncompressed form, but the site has a size limit on uploads.

    So I just fixed the link so that it points directly to the .cube file in my Dropbox folder. Let me know if you can make it work now.

  • Thank you, now it works. Very impressive! BTW, the file should be placed somewhere in $Path and $UserBaseDirectory with $BaseDirectory by default are not included in $Path. By default $HomeDirectory is included, so it would be better to recommend users to place the file in this directory.

  • Jason B says:

    Thanks for the help Alexey. I edited the post to be more clear.

  • max says:

    Thanks Jason. Good basis for a tool I’m writing.

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