=Configuration interaction (CI) spaces obtained from the full CI space by imposing arbitrary restrictions on the occupancies of molecular orbital (MO) groups are studied. It is proved that such restricted spaces are in a certain sense "closed." Namely, in the course of the Hamiltonian matrix construction the excitations out of the chosen restricted CI space may be easily replaced by the excitations within this space. 0 1996
Reactions of the gas-phase synthesis of tin vanadates, borates, and molybdates were studied. Standard enthalpies of formation and atomization of gaseous salts SnV 2 O 6 , SnB 2 O 4 , Sn 2 B 2 O 5 , SnMoO 4 , Sn 2 MoO 5 , and SnMo 2 O 7 were determined.
Approximate solution of the ensemble representability problem for density operators of arbitrary order is obtained. This solution is closely related to the "Q condition" of A. J. Coleman. The representability conditions are formulated in orbital representation and are easy to use. They are tested numerically on the base of CI calculation of simple atomic and molecular systems. General scheme of construction of the contraction operator right inverses is proposed and the explicit expression for the right inverse associated with the expansion operator is derived as an example. Two algorithms for direct 2-density matrix determination are described.
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