This is an Open Source framework for the Dynamic Radii Adjustment for COntinuum solvation (DRACO) approach. DRACO employs precomputed atomic partial charges and coordination numbers of the solute atoms to improve the solute cavity. As such, DRACO is compatible with major solvation models, improving their performance significantly and robustly at virtually no extra cost, especially for charged solutes.

The method is published in The Journal of Physical Chemistry Letters.

You can use the release binary of DRACO, or build your own version from source (see below). To do that, you need to clone the repository to your local environment.

git clone https://github.com/grimme-lab/DRACO.git
cd DRACO

The recommended version for building this project is using Meson.

To be able to build this project with Meson, you need version 0.60 or newer. To use the default backend, you also need ninja in version 1.7 or newer.

meson setup build --buildtype release
ninja -C build

You afterwards have to manually install the created binary in the path of your choice.

Once you obtained a functioning binary (either through building or by downloading a release binary), you can take a look at the possible options by invoking

draco --help

DRACO comes with an in-built interface to two efficient charge models (EEQ and CEH) via the light-weight tight-binding framwork tblite. A simple dynamic radii evulation is evoked, e.g. as

draco h2o.xyz --solvent water

Let's assume your xyz structure file looks like this:

3

o            0.00000000000000       -0.06365718653467       -0.00000000010001
h            0.77223547167307        0.50524694437309        0.00000000070010
h           -0.77223547197311        0.50524694397304        0.00000000030004

For this molecule, your output (default radii: cpcm, default qmodel: ceh) should look like this

           -------------------------------------------------
          |              Structure Information              |
           -------------------------------------------------

             Identifier  Partial Charge   Radii (unscaled)

                 O1          -0.29         1.16   (1.82)
                 H2           0.14         1.32   (1.32)
                 H3           0.14         1.32   (1.32)

After you obtained the dynamic radii from a DRACO calculation, you can use them in any QC program of your choice, that allows the usage of custom radii for the implicit solvent calculation.

Additionally, DRACO offers the possibility to automatically modify input files for the two QC program packages ORCA and TurboMole. To use this feature, you need to setup your input file as usual and afterwards invoke DRACO with e.g.

draco h2o.xyz --solvent water --prog orca inp_h2o

Given the following input file for a calculation with the CPCM solvation model using the ORCA program, DRACO will automatically rename the original file to inp_h2o.original and modify the respective input file by adding the dynamic radii.

%MaxCore 4000
! r2SCAN-3c RIJCOSX def2/jk defgrid2 cpcm(water)

* xyzfile 0 1 h2o.xyz

The resulting inp_h2o input file will look like this

%MaxCore 4000
! r2SCAN-3c RIJCOSX def2/jk defgrid2 cpcm(water)

* xyzfile 0 1 h2o.xyz

 %cpcm
  AtomRadii(0,  1.159790568642)
  AtomRadii(1,  1.318156186766)
  AtomRadii(2,  1.318156186761)
 end

This functionality also works for TurboMole and its corresponding control files.

DRACO is also build as a Fortran library and can therefore be easily included into Fortran projects by including the DRACOtype into your Fortran code. An in-depth example of this will be added in the near future. If you want to implement the DRACO approach into your Fortran code in the mean time, we are happy to help.