What is summoned is a change in the emotional state of the participants, which if performed correctly can make the task or event at hand more productive and enjoyable.
The meditation or invocation must be grounded in reality, such as calling the group to imagine themselves in the near future, on a peaceful walk through a park on a warm spring day; to imagine the world changed by the work about to begin; to consider the long-term results of their efforts.
Something along the lines that motivates the group to not lose focus on the goals, and to approach any disagreements with logic, facts and evidence, not adjectives and insinuations.
It's best to speak in a way that even seems reasonable to the religious members that stepped outside the room because they disapprove of an Atheist Invocation. Imagine how foolish they will look in the eyes of the members that stayed.
I personally wouldn't mention any other deities or make any salient insinuations about those who left the room. That would be unproductive.