First order
Concept
Note on an Approximation Treatment for Many-Electron Systems
1934 · CHR. KN. MØLLER, M. S. Plesset · Physical Review
A Simple Higher-Order Theory for Laminated Composite Plates
1984 · J. N. Reddy · Journal of Applied Mechanics
Geometry optimizations in the zero order regular approximation for relativistic effects
1999 · Erik van Lenthe, Andreas W. Ehlers, et al. · The Journal of Chemical Physics