@article{TMF_1973_14_1_a1,
     author = {A. M. Perelomov and V. S. Popov},
     title = {Variational principle for critical charge},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {18--26},
     publisher = {mathdoc},
     volume = {14},
     number = {1},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1973_14_1_a1/}
}