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DFT calculations with ADF
Density Functional Theory
• A detailed description of DFT will not be included in this
presentation.
• Notes which help to explain what keywords correspond
to will be included, but in a very loose, unrigourous way.
• For further details about DFT, the following books are
recommended. I also recommend you attend an
appropriate lecture series
– A chemists guide to DFT, W. Koch, M. C. Holthausen, Wiley-
VCH, ISBN: 3-527-30372-3
– Computational Chemistry, G.H. Grant, W. G. Richards, OUP
(Oxford Primer), ISBN: 978-0198557401
– Introduction to computational chemistry, F. Jensen, Wiley, ISBN:
0-470-01187-4
Amsterdam Density Functional
• ADF is a program used to do DFT
calculations
• www.scm.com is the website for the
program and includes
– Manual (under the documentation heading)
– Forum where people post problems and
others reply (under community)
• Also look on ccl.net, although this is more
general and ADF issues tend to get
directed to the ADF website.
Example input file
$ADFBIN/adf -n 1 <<eor
TITLE H2O
BASIS
TYPE TZP
CORE Small
END
SCF
ITERATIONS 99
CONVERGE 0.000001
END
GEOMETRY
optim
END
INTEGRATION 6.0
XC
GRADIENT OPBE
END
CHARGE 0 0
ATOMS
O 0.000000 0.000000 0.012976
H 0.000000 -0.754442 -0.589982
H 0.000000 0.754442 -0.589982
END
ENDINPUT
eor
Example input file - explained
$ADFBIN/adf -n 1 <<eor This line needs to be included in all ADF calculations
TITLE H2O
Folder where Use ADF executable Use one processor
BASIS ADF binaries (there are others for
TYPE TZP (irrelevant for machines
CORE Small are kept different programs
END with only 1 cpu)
and utilities)
SCF
ITERATIONS 99
CONVERGE 0.000001
END
Read this file until
GEOMETRY you reach “eor”
optim
END
INTEGRATION 6.0
XC
GRADIENT OPBE
END
CHARGE 0 0
ATOMS
O 0.000000 0.000000 0.012976
H 0.000000 -0.754442 -0.589982
H 0.000000 0.754442 -0.589982
END
ENDINPUT Specifies the input file is finished
eor
Stop reading the file (see first line)
Example input file - explained
$ADFBIN/adf -n 1 <<eor
TITLE H2O You can give your calculation whatever title you like or
exclude this keyword altogether
BASIS
TYPE TZP
CORE Small
BASIS keyword specifies what type of basis set you want
END to use.
SCF TYPE can be lower case but TZP (or whatever you
ITERATIONS 99 choose) must be capitals as it points to a directory
CONVERGE 0.000001 CORE specifies how large your frozen core is, case
END
specific
GEOMETRY
optim
END specifies that this is the end of this section
END
SCF specifies the conditions for putting the electron
INTEGRATION 6.0
density correctly
XC
GRADIENT OPBE
Iterations says how many cycles it has to converge in
END Converge says how much the energy is allowed to change
CHARGE 0 0 by to be considered converged
ATOMS
O 0.000000 0.000000 0.012976
H 0.000000 -0.754442 -0.589982
H 0.000000 0.754442 -0.589982
END
ENDINPUT
eor
Some definitions
• BASIS SET
– These are mathematical functions which describe
where the electron density is allowed to go. The
proportion of each function can be varied until the
energy provided by the electron density is minimised.
In ADF the basis functions are the shape of s, p, d etc
orbitals
• FROZEN CORE
– The innermost electrons of an element contribute a
great deal to the overall energy but are largely
unaffected by the overall environment of the atom.
Therefore they can be optimised once and then kept
the same throughout the calculation as the valence
electrons are the ones which change most.
Some definitions
• Self Consistent Field (SCF)
– This is how the electron density is distributed
within the field of the nuclei and other
electrons. An iterative procedure is used to
assign the electron density until it is internally
consistent, and changing the position of one
electron a tiny bit does not change the energy
overall.
Example input file - explained
$ADFBIN/adf -n 1 <<eor
TITLE H2O
BASIS Geometry keyword specifies whether you want to optimise
TYPE TZP
CORE Small
the geometry, do a single point, or do frequencies. It can
END also specify convergence criteria.
SCF
ITERATIONS 99
CONVERGE 0.000001
Integration relates to the accuracy of the calculation.
END
GEOMETRY The XC keyword is used to select the functional to be used
optim
END
INTEGRATION 6.0
The charge keyword specifies the charge of the molecule and
the number of unpaired electrons. If there are unpaired
XC
GRADIENT OPBE
electrons another keyword, UNRESTRICTED, needs to be
END included on another line
CHARGE 0 0
ATOMS
O 0.000000 0.000000 0.012976
H 0.000000 -0.754442 -0.589982
H 0.000000 0.754442 -0.589982
END
ENDINPUT
eor
Some definitions
• Functional
– A functional is a function that acts on the basis
functions to return the energy. It can be thought of
that in the Schrödinger equation the Hamiltonian acts
on the wavefunction to give the energy multiplied by
the wavefunction. In DFT, the functional acts on the
electron density (in the form of basis sets) to give the
energy multiplied by the electron density. However,
the exact form the functional should take is unknown
so many different functionals have been created
which all give slightly different results.
Some definitions
• RESTRICTED/UNRESTRICTED
– In a calculation where there are no unpaired
electrons, the spin-up and spin-down
electrons are energetically and spatially
identically.
– In a calculation where there are unpaired
electrons (multiplicity > 1), the spin-up and
spin-down electrons need to be able to have
different energetic and spatial properties, and
the UNRESTRICTED keyword allows this.
Example input file - explained
$ADFBIN/adf -n 1 <<eor
TITLE H2O
BASIS
TYPE TZP
CORE Small
END
SCF
ITERATIONS 99
CONVERGE 0.000001 Atoms keyword is where the geometry of the
END
molecule (location of nuclei) is included.
GEOMETRY Can be xyz file or z-matrix (in which case the
optim
END word internal or zmat needs to be included
INTEGRATION 6.0 after word atoms)
XC
GRADIENT OPBE
END
CHARGE 0 0
ATOMS
O 0.000000 0.000000 0.012976
H 0.000000 -0.754442 -0.589982
H 0.000000 0.754442 -0.589982
END
ENDINPUT
eor
Example output file
• Output files are rather large so here is a summary of what is in an output
file
• Energy
Summary of Bonding Energy (energy terms are taken from the energy decomposition above)
======================================================================================
Electrostatic Energy: -0.256031610040912 -6.9670 -160.66 -672.21
Kinetic Energy: 0.447024581673579 12.1642 280.51 1173.66
Coulomb (Steric+OrbInt) Energy: -0.247468564515559 -6.7340 -155.29 -649.73
XC Energy: -0.468398583755849 -12.7458 -293.92 -1229.78
-------------------- ----------- ---------- -----------
Total Bonding Energy: -0.524874176638742 -14.2826 -329.36 -1378.06
Hartree Electron Volt Kcal mol-1 kJ mol-1
If you want to see which structures are more stable then it is the energies you
want to compare.
You can only compare energies from the same method (functional, basis set,
level of integration) and number of atoms/atom types.
ADF calculates the energy of bringing different atoms together, i.e. the bonding
energy.
Looking at results
• Chemcraft (www.chemcraftprog.com)
– Still need to double check that this can read
ADF2008 output correctly (It does read it but I
am not sure if it reads the last geometry)
• Can view iccg wiki too for some general
details (www.warwick.ac.uk/go/iccg)
• Open up file.output using chemcraft
• Last structure in optimisation displayed
• Can also display frequencies
