ML SION1

ML_SION1 = [real]
Default: ML_SION1 = 0.5 

Description: This tag specifies the width $\sigma _{\text{atom}}$ of the Gaussian functions used for broadening the atomic distributions of the radial descriptor $\rho _{i}^{(2)}(r)$ within the machine learning force field method.

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The radial descriptor is constructed from

$\rho _{i}^{(2)}\left(r\right)={\frac {1}{4\pi }}\int \rho _{i}\left(r{\hat {\mathbf {r} }}\right)d{\hat {\mathbf {r} }},\quad {\text{where}}\quad \rho _{i}\left(\mathbf {r} \right)=\sum \limits _{j=1}^{N_{\mathrm {a} }}f_{\mathrm {cut} }\left(r_{ij}\right)g\left(\mathbf {r} -\mathbf {r} _{ij}\right)$

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_SION1 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 somewhat system-dependent. For instance, a smaller value for ML_SION1 can increase the number of local reference configurations, and hence ultimately the quality of the MLFF. See also here.

The unit of ML_SION1 is $\mathrm {\AA}$.

Related tags and articles

ML_LMLFF, ML_SION2, ML_RCUT1, ML_RCUT2, ML_MRB1, ML_MRB2

Examples that use this tag

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