Nassella (Stipa) tenuissima is a great choice for this circular bed surrounding Joan Miró's Moonbird. The Sculpture Garden of the Hirshhorn Museum has undergone several redesigns since it first opened in 1974. I remember them only vaguely, but I do like the plantings now. Some are sculptural themselves, dwarf pines and Hinoki Cypress cultivars. Others, like the grass in this picture, one of my favorites, provide context without intruding. Distinctively textural, it moves horizontally without distracting or detracting in any way from the sculpture. This piece, Moonbird, when I have seen it other places on paving in a cityscape has always felt oddly out of place. Of course that may be the point of the sculpture!
Mexican Feather Grass is one of those plants that, once you see it, you have to have it. At least it is for a lot of people. Native to, surprise, Mexico and the SW United States, it prefers well-drained soil and handles drought with no problems at all. I have grown it in full sun next to the street for at least 10 years though we must be near the northern limit of its range. One plant, isolated enough to show its form, is a sculpture unto itself. I think I have heard it called Horsetail grass, and it does resemble a horse's tail. The blades are very fine and the slightest breeze is enough to shift the plant. It doesn't qualify as even a "near native", but I grow it anyway. The literature suggests that it can reseed enough to become weedy; my plant has never seeded, but perhaps that would require water. If you plant it, and it does begin to seed around, just remove the seed heads before they ripen. They aren't really a visual asset so there's no harm and unless you have a large planting it is doable.
Despite its widespread appeal, local garden centers don't stock it in any quantity. They seem to have 20 or 30 pots a year. You have to get lucky to find it before it's sold out. Because it moves so quickly in a retail environment, it has caught the attention of the big Box Stores and they seem to be contracting it in quantity. I noticed a entire cartfull at my local (White Oak) Home Depot last year, but it goes just as quickly there; it was gone in a few days! There's always on-lin, where it's widely stocked.