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Table of contents

Table of Contents
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What is COSMO?

TURBOMOLE includes the Conductor-like Screening Model (COSMO) which is a continuum solvation model. In this approach, the solvent is represented by a dielectric continuum with permittivity ε and the solute molecule forms a cavity within this continuum (see TURBOMOLE manual chapter 18 for more details and original literature references). 

Using COSMO for anionic systems

One very important use case for the COSMO solvent field is anionic systems with charge higher than –1. Kohn-Sham DFT has major issues in describing such anions and typically yields positive energies for the highest occupied orbitals (that is, the electrons are not actually bound). This issue can be solved by using COSMO solvent field to counter the anionic charge of the system. Adding the dielectric continuum around the anion normally leads in a better description of the electronic structure.

The permittivity ε could in principle set to the literature value of any solvent. However, in particular when the solvent field is only used to counter the anionic charge of the system, it is recommended to keep it in the default value (ε = ∞).

How to use COSMO in a geometry optimization?

To turn on COSMO, first run define normally. After that, add the following keyword to the beginning of the control file:

...

This will turn on COSMO with default settings. You can submit the geometry optimization normally.

Frequency calculations with COSMO

If you are using COSMO and want to run frequency calculation, it is recommended to run a numerical frequency calculation with NumForce instead of aoforce. You need to use -cosmo switch and you cannot use -c switch:

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The -c switch does not work with -cosmo because COSMO needs data from the gradient check run.

Complete example

This example is based on [Si9(SnCy3)2]2– published in Chem. Sci., 2019, 10, 9130 (DOI). XYZ coordinates for the example system are available here: si9_sncy3_2_2m.xyz. Note that these coordinates are for an unoptimized geometry.

Creating input files with define

Start by creating a new empty directory and copy the XYZ file there. Then, conver the XYZ file to a coord file:

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But you can edit the file in any way you like!

Submitting the geometry optimization job

The job can now be submitted:

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cycle = 1 SCF energy = -4443.7882441900 |dE/dxyz| = 0.003630

Analysis of the geometry optimization job

Confirm that you have file GEO_OPT_CONVERGED in the directory. It is also a good practice to check how the optimization has behaved with

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Submitting a frequency calculation job

Submit a numerical frequency calculation with COSMO:

jsub -np 12 -smp -mem 2G tm si9_sncy3_2_2m_pbe0_tzvp_fq jNumForce -ri -central -cosmo

Analysis of the frequency calculation job

Check vibspectrum, no imaginary modes

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