Inherent restrictions of the Hylleraas-Undheim-MacDonald higher roots, and minimization functionals at the excited states. - Naoum C. Bacalis; Z. Xiong; Dimitrios Karaoulanis (J. Comput. Methods Sci. Eng., 2008)

Minimization principle for non degenerate excited states (independent of orthogonality to lower lying known approximants). - Naoum C. Bacalis (J. Comput. Methods Sci. Eng., 2016)

Correct small-truncated excited state wave functions obtained via minimization principle for excited states compared/ opposed to Hylleraas-Undheim and McDonald higher "roots". - Z. Xiong; J. Zang; H. J. Liu; Dimitrios Karaoulanis; Q. Zhou; Naoum C. Bacalis (J. Comput. Methods Sci. Eng., 2017)