Calculating EVI with S2A data

I am calculating EVI with S2A data using this formula in the band math of SNAP —> G*(NIR-Red)/(NIR+C1*Red - C2 * Blue +L) . The constants G, C1, C2 and L are 2.5, 6, 7.5 and 1 respectively when using MODIS and Landsat Data. G is a scaling factor and C1, C2, L are coefficients of atmospheric condition.

What are the corresponding constants when using Sentinel-2A data? In using this index, the bands must be atmospherically corrected. Can anyone guide me on converting sentinel-2A data to reflectance values? Or is S2A product delivered already corrected atmospherically? Thanks!

S2A data is not atmospherically corrected. It provides TOA reflectances but you have to divide by 10000 first.
Please have a look at the Sentinel-2 Products Specification Document (PSD) which you can find in the document library.