The other variable is the basis set; here, we refer to a basis set
of one-electron functions (or orbitals), usually centered on
the atoms. The electronic Schrödinger
equation becomes greatly simplified once we solve it using such a basis.
The larger the basis set (the more orbitals it contains), the more
accurately we model the Schrödinger equation *for the given
correlation method*. However, even an infinite basis set can give
incorrect answers when paired with an approximate treatment of electron
correlation. Likewise, even an exact treatment of electron correlation can
give terrible answers when paired with a very small basis set. Better and
better results can be obtained when one increases the basis set *and*
improves the treatment of correlation. In the limit of an infinite basis
set and an exact treatment of electron correlation, the electronic
Schrödinger equation would be solved exactly.