Recent Progress in the Variational Orbital Approach to Atomic and Molecular Electronic Structure

Unexpected properties of non‐autoionizing doubly excited states of the H2 molecule

“…Since the same basis set must adequately represent 40 states, each one with even or odd parity and triplet or singlet multiplicity, some compromise must be accepted. Nevertheless, the results for the 40 states reported in the first three columns of Tables are of satisfactory quality and compare well with the best available results; indeed, the largest error, 3 × 10 −5 E h , is for the first 3 P e state, with electronic configuration 2p2p. Better results can be achieved by extending the basis set to higher n ℓ functions, but, as already stated, our goal is not an optimal basis for a single state.…”

“…Nevertheless, the results for the 40 states reported in the first three columns of Tables are of satisfactory quality and compare well with the best available results; indeed, the largest error, 3 × 10 −5 E h , is for the first 3 P e state, with electronic configuration 2p2p. Better results can be achieved by extending the basis set to higher n ℓ functions, but, as already stated, our goal is not an optimal basis for a single state. The basis set orbital exponents are: 2p = 1.86, 1.142, 0.5, 0.16; 3p = 1.168, 0.7, 0.333333, 0.05; 4p = 0.65, 0.25, 0.025; 5p = 0.7, 0.2, 0.04; 6p = 0.166667; 3d = 1.15, 0.75, 0.333333, 0.078; 4d = 0.65, 0.25, 0.06; 5d = 0.8, 0.2, 0.05; 6d = 0.9, 0.166667, 0.04; 4f = 1.688, 1.53, 0.25, 0.08; 5d = 0.572, 0.3033, 0.2, 0.07; 6d = 0.93, 0.4, 0.166667, 0.06; 5g = 0.672, 0.365, 0.2, 0.05; 6g = 0.844, 0.406, 0.166667, 0.04; 6h = 2.18, 1.9, 1.0, 0.166667, 0.04.…”

Configuration Interaction Study of the 3 P Ground State of the Carbon Atom

“…In a recent volume celebrating the 100 th anniversary of the birth of Per-Olov Löwdin, one of his students, Carlos F. Bunge, dedicated a chapter to him [15]. Another chapter about the state of the art in highly accurate CI calculations on atoms and molecules [16] is also recommended.…”

“…This becomes important for very accurate CI calculations, as reported e.g. by Bunge [16]. In our work, we have constructed the configurations as linear combinations of all different terms occurring in the different degenerate configuration, see Table 1.…”

Seniority based energy renormalization group (Ω-ERG) approach in quantum chemistry: Initial formulation and application to potential energy surfaces

“…Since FCI approach is associated with exponential computational scaling, much research has been focused on the development of less computationally demanding ab initio methods for strongly correlated molecular systems. Examples of such methods include: truncated (limited) CI methods and CI methods with various extrapolations [63][64][65][66][67][68][69][70][71][72][73][74], multireference coupled cluster (CC) methods [75][76][77][78][79][80], iterative variational approaches [81][82][83][84][85][86], various methods based on density-matrices [87][88][89][90], matrix product states (MPS) and tensor product states (TPS)-based approaches [91][92][93][94][95] which include popular density-matrix renormalization group (DMRG) method [96][97][98][99][100][101][102][103][104][105][106][107]…”