How to parse and write

This page outlines the various ways cclib can be used to parse and write logfiles, and provides several examples to get you started.

From Python

Importing cclib and parsing a file is a few lines of Python code, making it simple to access data from the output file of any supported computational chemistry program. For example:

>>> import cclib

>>> filename = "water.out"
>>> parser =
>>> data = parser.parse()
>>> print("There are %i atoms and %i MOs" % (data.natom, data.nmo))

There are 3 atoms and 7 MOs

A newer command, ccread, combines both the format detection and parsing steps:

>>> import cclib

>>> filename = "logfile.out"
>>> data =
>>> print("There are %i atoms and %i MOs" % (data.natom, data.nmo))

There are 3 atoms and 7 MOs

The data object above contains all the information cclib was able to to parse from the output file, available as attributes on the object:

>>> dir(data)

[(...), 'atomcoords', 'atommasses', 'atomnos', 'charge', (...), 'mult', 'natom, 'nbasis', ...]

You can find a full list of these attribute on the parsed data page.

From command line

The cclib package provides four scripts to parse and write data: ccget, ccwrite, cda, and ccframe.

  1. ccget is used to parse attribute data from output files.

  2. ccwrite has the ability to list out all valid attribute data that can be parsed from an output format. It has the added feature of writing the output file into four different formats i.e. json, cjson, cml, xyz.

  3. cda is used for the chemical decomposition analysis of output files.

  4. ccframe is used to write data tables from output files.

This page describes how to use the ccget, ccwrite and ccframe scripts to obtain data from output files.


The data types that can be parsed from the output file depends on the type of computation being conducted. The name of the output file used to show example usage is Benzeneselenol.out.

Data type can be parsed from the output file by following this format:

ccget <attribute> [<attribute>] <CompChemLogFile> [<CompChemLogFile>]

where attribute can be any one of the attribute names available here.

  1. Atomic Charges

    The atomic charges are obtained by using the atomcharges attribute:

    $ ccget atomcharges Benzeneselenol.out
    Attempting to read Benzeneselenol.out
    {'mulliken': array([-0.49915 ,  0.056965,  0.172161,  0.349794, -0.153072,  0.094583,
        0.016487,  0.050249,  0.002149,  0.01161 ,  0.053777, -0.173671,
  2. Electronic Energies

    The molecular electronic energies after SCF (DFT) optimization of the input molecule are printed by using the scfenergies attribute:

    $ ccget scfenergies Benzeneselenol.out
    Attempting to read Benzeneselenol.out
    [-71671.43702915 -71671.4524142  -71671.4534768  -71671.45447492
    -71671.4556548  -71671.45605671 -71671.43194906 -71671.45761021
    -71671.45850275 -71671.39630296 -71671.45915119 -71671.45935854
    -71671.4594614  -71671.45947338 -71671.45948807 -71671.4594946
    -71671.4594946 ]
  3. Geometry Targets

    The targets for convergence of geometry optimization can be obtained by using the geotargets attribute:

    $ ccget geotargets Benzeneselenol.out
    Attempting to read Benzeneselenol.out
    [ 0.00045  0.0003   0.0018   0.0012 ]

Chaining of attributes

ccget provides the user with the option to chain attributes to obtain more than one type of data with a command call. The attributes can be chained in any particular order. A few chained examples are provided below.

  1. Molecular Orbitals and Multiplicity

    The number of molecular orbitals and the number of basis functions used to optimize the molecule can be obtained by running the following command:

    $ ccget nmo nbasis Benzeneselenol.out
    Attempting to read Benzeneselenol.out
  2. Enthalpy and Vibrational Frequency

    The enthalpy and the vibrational frequencies of the optimized molecule is conducted is obtained below:

    $ ccget enthalpy vibfreqs Benzeneselenol.out
    Attempting to read Benzeneselenol.out
    [  129.5512   170.6681   231.4278   304.8614   407.8299   472.5026
       629.9087   679.9032   693.2509   746.7694   812.5113   850.2578
       915.8742   987.1252   988.1785  1002.8922  1038.1073  1091.4005
      1102.3417  1183.3857  1209.2727  1311.3497  1355.6441  1471.4447
      1510.1919  1611.9088  1619.0156  2391.2487  3165.1596  3171.3909
      3182.0753  3188.5786  3198.0359]


The same Benzeneselenol.out file used in the previous examples will be used as the input file for ccwrite. When the ccwrite script is used with a valid input, it prints out the valid attributes that can be parsed from the file.

Command line format:

ccwrite <OutputFileFormat>  <CompChemLogFile> [<CompChemLogFile>]

The valid output file formats are cjson, cml, and xyz.

  1. Chemical markup language (CML):

    $ ccwrite cml Benzeneselenol.out
    Attempting to parse Benzeneselenol.out
    cclib can parse the following attributes from Benzeneselenol.out:

A Benzeneselenol.cml output file is generated in the same directory as the Benzeneselenol.out file:

<?xml version='1.0' encoding='utf-8'?>
<molecule id="Benzeneselenol.out" xmlns="">
    <atom elementType="C" id="a1" x3="-2.8947620000" y3="-0.0136420000" z3="-0.0015280000" />
    <atom elementType="C" id="a2" x3="-2.2062510000" y3="1.1938510000" z3="-0.0025210000" />
    <atom elementType="C" id="a3" x3="-0.8164260000" y3="1.2153020000" z3="-0.0022010000" />
    <atom elementType="C" id="a4" x3="-0.1033520000" y3="0.0183920000" z3="0.0031060000" />
    <atom elementType="C" id="a5" x3="-0.7906630000" y3="-1.1943840000" z3="0.0058500000" />
    <atom elementType="C" id="a6" x3="-2.1799570000" y3="-1.2059710000" z3="0.0017890000" />
    <atom elementType="H" id="a7" x3="-3.9758430000" y3="-0.0253010000" z3="-0.0029040000" />
    <atom elementType="H" id="a8" x3="-2.7502340000" y3="2.1291370000" z3="-0.0052760000" />
    <atom elementType="H" id="a9" x3="-0.2961840000" y3="2.1630180000" z3="-0.0073260000" />
    <atom elementType="H" id="a10" x3="-0.2474670000" y3="-2.1302310000" z3="0.0132260000" />
    <atom elementType="H" id="a11" x3="-2.7028960000" y3="-2.1530750000" z3="0.0036640000" />
    <atom elementType="Se" id="a12" x3="1.8210800000" y3="-0.0433780000" z3="-0.0038760000" />
    <atom elementType="H" id="a13" x3="2.0043580000" y3="1.4100070000" z3="0.1034490000" />
    <bond atomRefs2="a9 a3" order="1" />
    <bond atomRefs2="a8 a2" order="1" />
    <bond atomRefs2="a12 a4" order="1" />
    <bond atomRefs2="a12 a13" order="1" />
    <bond atomRefs2="a7 a1" order="1" />
    <bond atomRefs2="a2 a3" order="2" />
    <bond atomRefs2="a2 a1" order="1" />
    <bond atomRefs2="a3 a4" order="1" />
    <bond atomRefs2="a1 a6" order="2" />
    <bond atomRefs2="a6 a11" order="1" />
    <bond atomRefs2="a6 a5" order="1" />
    <bond atomRefs2="a4 a5" order="2" />
    <bond atomRefs2="a5 a10" order="1" />
  1. XYZ

Using xyz as the <OutputFileFormat> with Benzeneselenol.out, we obtain the following file:

Benzeneselenol.out: Geometry 17
C     -2.8947620000   -0.0136420000   -0.0015280000
C     -2.2062510000    1.1938510000   -0.0025210000
C     -0.8164260000    1.2153020000   -0.0022010000
C     -0.1033520000    0.0183920000    0.0031060000
C     -0.7906630000   -1.1943840000    0.0058500000
C     -2.1799570000   -1.2059710000    0.0017890000
H     -3.9758430000   -0.0253010000   -0.0029040000
H     -2.7502340000    2.1291370000   -0.0052760000
H     -0.2961840000    2.1630180000   -0.0073260000
H     -0.2474670000   -2.1302310000    0.0132260000
H     -2.7028960000   -2.1530750000    0.0036640000
Se     1.8210800000   -0.0433780000   -0.0038760000
H      2.0043580000    1.4100070000    0.1034490000


This script creates complete tables of data from output files in some of the formats supported by pandas. Since the pandas library is not a dependency of cclib, it must be installed separately.

A complete data table can be parsed from many output files by following this format:

ccframe [--force|-f] -O <OutputDest> <CompChemLogFile> [<CompChemLogFile>...]

The argument for -O indicates the data file to be written and its extension specifies the filetype (e.g. csv, h5/hdf/hdf5, json, pickle/pkl, xlsx). An error will be thrown if <OutputDest> already exists, but you can force overwriting by using the --force (or -f) flag. Since higher-dimensional attributes (e.g. atomcoords) are handled as plain text in some file formats (such as Excel XLSX or CSV), we recommend storing JSON or HDF5 files. Observe that the output data file is overwritten if it exits already.