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[[_TOC_]]
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# Selecting the functional
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The functional must be selected at compilation stage in *predefines.h* file:
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```c
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/**
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| ... | ... | @@ -92,9 +95,15 @@ The BdG functional is equivalent to Bogoliubov de-Gennes mean-field approximati |
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\frac{\tau_{\downarrow}}{2}
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+ g\nu^{\dagger}\nu
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```
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The (bare) coupling constant $`g`$ is related to scattering length by the formula $`g=4\pi\hbar^2a/m`$.
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The (bare) coupling constant $`g`$ is related to scattering length by the formula $`g=4\pi\hbar^2a/m_r`$, where $`m_r`$ is reduced mass.
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Below we provide predictions of BdG functional for total energy and paring gap as a function of coupling constant $`-ak_F`$ computed for uniform and spin-symmetric system. Results are compared with predictions of BCS theory, and as expected the agreement is observed for $`-ak_F<1`$.
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# Regularization scheme of pairing field
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By default, W-SLDA implements a regularization scheme of the pairing field known as Superfluid Local Density Approximation (SLDA). Precisely, the implemented formulas are (9.86)-(9.87) from paper [arXiv:1008.3933](https://arxiv.org/abs/1008.3933).
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*Note 1*: The regularization scheme is only valid for 3D systems. If you want to execute pure 2D or 1D calculations, you need to provide your regularization procedure. For more info see [Strict 2D or 1D modes](Strict 2D or 1D mode).
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*Note 2*: The regularization uses average effective mass $`\alpha_{+}`$ and average chemical potential $`\mu_{+}`$. Thus, the regularization is valid for spin-imbalanced and mass-imbalanced systems as well. |
