Compact Hylleraas-type wavefunctions for the lithium isoelectronic sequence

Compact Hylleraas-type wavefunctions of three types, denoted A, B and C, are constructed for the 2S ground states of the lithium atom and its isoelectronic ions Be+, B2+,…,Si11+. All the exponents and powers of the basis functions are optimized. The 20-term type B and 50-term type C wavefunctions are as accurate as several significantly larger expansions reported in the literature. The 50-term type C wavefunctions predict energies accurate to better than 3 parts in 107.