ML SION2

ML_SION2 = [real]
Default: ML_SION2 = ML_SION1 

Description: This tag specifies the width $\sigma _{\text{atom}}$ of the Gaussian functions used for broadening the atomic distributions of the angular descriptor $\rho _{i}^{(3)}(r)$ within the machine learning force field method.

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The angular descriptor is constructed from

$\rho _{i}^{(3)}\left(r,s,\theta \right)=\iint d{\hat {\mathbf {r} }}d{\hat {\mathbf {s} }}\delta \left({\hat {\mathbf {r} }}\cdot {\hat {\mathbf {s} }}-\mathrm {cos} \theta \right)\sum \limits _{j=1}^{N_{a}}\sum \limits _{k\neq j}^{N_{a}}\rho _{ik}\left(r{\hat {\mathbf {r} }}\right)\rho _{ij}\left(s{\hat {\mathbf {s} }}\right),\quad {\text{where}}\quad \rho _{ij}\left(\mathbf {r} \right)=f_{\mathrm {cut} }\left(r_{ij}\right)g\left(\mathbf {r} -\mathbf {r} _{ij}\right)$

and $g\left(\mathbf {r} \right)$ is the following approximation of the delta function:

$g\left(\mathbf {r} \right)={\frac {1}{\sqrt {2\sigma _{\mathrm {atom} }\pi }}}\mathrm {exp} \left(-{\frac {|\mathbf {r} |^{2}}{2\sigma _{\mathrm {atom} }^{2}}}\right).$

The tag ML_SION2 sets the width $\sigma _{\text{atom}}$ of the above Gaussian function (see this section for more details).

Tip: Our test calculations indicate that ML_SION1 = ML_SION2 results in an optimal training performance. Furthermore, a value of 0.5 was found to be a good default value for both. However, the best choice is system-dependent, careful testing may improve machine learning results.

The unit of ML_SION2 is $\mathrm {\AA}$.

Related tags and articles

ML_LMLFF, ML_SION1, ML_RCUT1, ML_RCUT2, ML_MRB1, ML_MRB2

Examples that use this tag

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