[Ifeffit] Create Atoms input with just coordinates

Hi, I am trying to create an Atoms input file for actinium. Since not a lot is known about this element we run some DT calculations. One molecule of Ac acetate in a box surrounded by water. I have the coordinate of each elements. I was told the symmetry was P1 (I guess for the box) but unfortunately their is no symmetry in liquid and thus we cannot input the cell parameters (distances a, b, c and angles alpha, beta, gamma). I was wondering if their were a way to make Atoms run to obtain the Feff calculations. Or we should use a different model with a known solid? Thank you for your help Maryline Ferrier