Boston Lyric Opera has received a $5 million gift from the Calderwood Charitable Foundation, both organizations have announced. The gift will endow BLO’s top leadership position, currently held by Esther Nelson, which will now be designated as the Stanford Calderwood General and Artistic Director. According to Steven P. Akin, chairman of BLO’s board, the gift is the single largest institutional contribution in the organization’s 39-year history. BLO’s new production of Mozart’s “Don Giovanni” opens on Friday and runs through May 10.