[DFTB-Plus-User] How to run a organic radical cation

Ben Hourahine benjamin.hourahine at strath.ac.uk
Mon Aug 12 13:02:44 CEST 2019

Hello Francisco,

apologies for the delay in replying. The spin constants are for the
atoms and are required for any spin-polarized calculation (there is a
table in the back of the manual for some parameters, but the
Slater-Koster parameter files usually come with a list in their
documentation). The multiplicity is set by choosing the number of
unpaired spins in the system instead of directly setting multiplicity
(this is more general, as systems can have fractional spin in some cases).

A minimal example input for H2+ would look like:

Geometry = GenFormat {
2  C
     1 1 0.0 0.0 0.0
     1 1 0.0 0.0 0.7

Hamiltonian = DFTB {
  SCC = Yes
  MaxAngularMomentum = {
    H = "s"
  Charge = +1
  SpinPolarisation = Colinear {
    UnpairedElectrons = 1 # doublet state
  SpinConstants = {
    H = {
  SlaterKosterFiles = {
    H-H = "H-H.skf"

Note that unless you use shell resolved spin polarisation (check the
manual, or examples from the autotest directory), you only give the spin
constants for the highest occupied atomic orbital for each species.

The constrained charge feature you mention was present in an earlier
version of the code, but was removed. It will probably make a return in
the next code release (19.2) late this year.



On 31/07/2019 02:26, Francisco Adasme wrote:
> Dear DFTB+ members,
> I'm interested in doing some SCC calculations on an organic molecule
> in a radical cation state. In pure QM software, I'd set the charge to
> 1 and multiplicity to 2. What options should I set to model this since
> there is no multiplicitykeyword?I found this answer
> <https://mailman.zfn.uni-bremen.de/pipermail/dftb-plus-user/2012/000913.html>referring
> to the SpinPolarisation option, which also needs SpinConstants, but I
> don't know what values to use.
> Additionally, is there a way to constrain the charge to a specified
> molecular fragment?, as I note that other programs support this.
> Best regards,
> Francisco.
> -- 
> Francisco Adasme Carreño
> Bioinformatics Engineer, PhD
> Center for Bioinformatics and Molecular Simulations, CBSM
> Universidad de Talca
> Av. Lircay S/N, Talca, Chile
> T: (+56) 71 2 201 798
> E: francisco.adasme at gmail.com <mailto:francisco.adasme at gmail.com> or
> fadasmec at utalca.cl <mailto:fadasmec at utalca.cl>
> URL: http://about.me/franciscoadasme,
> https://www.researchgate.net/profile/Francisco_Adasme
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        Dr.  B.  Hourahine,  Senior  lecturer
            SUPA, Department  of  Physics,
             University  of  Strathclyde,
              John  Anderson  Building,
          107 Rottenrow, Glasgow G4 0NG, UK.                  
  +44 141 548 2325, benjamin.hourahine at strath.ac.uk

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