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

${\rho }_i^{(3)}(r,s,\theta )=\iint d\widehat{\mathbf{𝐫}}d\widehat{\mathbf{𝐬}}\delta (\widehat{\mathbf{𝐫}}\cdot \widehat{\mathbf{𝐬}}-\mathrm{c}\mathrm{o}\mathrm{s}\theta )\sum _{j=1}^{N_a}\sum _{k\ne j}^{N_a}{\rho }_{ik}\left(r\widehat{\mathbf{𝐫}}\right){\rho }_{ij}\left(s\widehat{\mathbf{𝐬}}\right),\text{where}{\rho }_{ij}\left(\mathbf{𝐫}\right)=f_{\mathrm{c}\mathrm{u}\mathrm{t}}\left(r_{ij}\right)g(\mathbf{𝐫}-{\mathbf{𝐫}}_{ij})$

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

$g\left(\mathbf{𝐫}\right)=\frac{1}{\sqrt{2{\sigma }_{\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}}\pi }}\mathrm{e}\mathrm{x}\mathrm{p}(-\frac{|\mathbf{𝐫}{|}^2}{2{\sigma }_{\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}}^2}).$

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 $\AA$.

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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