Look at this answer Tehillim on Shabbos, which says from R' Shlomo Zalman Auerbach that one may say Tehillim on Shabbos for one that is sick if it is done privately. My question is how to reconcile this with the fact that one of the ways tehillim is divided up, is in days of the week including Shabbos. This makes it sound like it is lchatchila to say the Shabbos portion on Shabbos, not only in certain circumstances. Is there a difference which portion you are saying? Is there a difference if you are saying tehillim for spiritual or material needs?