The stalker_ost_main_theme.zip file you have requested: Clear Sky / Mods / Sound and Music / STALKER MOVIE - Original soundtrack theme for menu - 1.69mb is not available. Perhaps try browsing all files for the game S.T.A.L.K.E.R.: Clear Sky and upload any files you want to share or are missing. This is the only information we could locate:
Since the S.T.A.L.K.E.R. game-series is vaguely based on the 1979 motion picture "STALKER" (Dir. Andrei Tarkovsky, 1979) The music fits right in. It's really an amazing movie as well as an awesome and haunting original soundtrack.