Density matrix renormalization group calculations on relative energies of transition metal complexes and clusters

Abstract

The accurate first-principles calculation of relative energies of transition metal complexes and clusters is still one of the great challenges for quantum chemistry. Dense lying electronic states and near degeneracies make accurate predictions difficult, and multireference methods with large active spaces are required. Often density functional theory calculations are employed for feasibility reasons, but their actual accuracy for a given system is usually difficult to assess (also because accurate ab initio reference data are lacking). In this work we study the performance of the density matrix renormalization group algorithm for the prediction of relative energies of transition metal complexes and clusters of different spin and molecular structure. In particular, the focus is on the relative energetical order of electronic states of different spin for mononuclear complexes and on the relative energy of different isomers of dinuclear oxo-bridged copper clusters.

The restricted active space followed by second-order perturbation theory method: Theory and application to the study of CuO2 and Cu2O2 systems

“…The lack of Cu 3d-4d correlation in the zeroth-order wave function is the main reason for the failure of the CASPT2 treatment in the original 41 and later 47,49,68 CASPT2 studies on this subject. All these studies were performed with moderately sized basis sets ͑comparable to BS1͒ and with active spaces starting from the ͑8 in 6͒ space used here, possibly extended with other valence ͑O 2s, O 2p z ͒ or virtual ͑O 3p orbitals͒ orbitals.…”

Spin-adapted density matrix renormalization group algorithms for quantum chemistry

“…chemistry. 8,11,[17][18][19][20][21] Here, the ability to utilise spin symmetry is an important advantage. This is because the large number of unpaired electrons often leads to many low lying spin states in a very narrow energy window, which can only be efficiently resolved by targeting a specific spin sector.…”

“…[6][7][8][9][10][11] After early attempts to use the DMRG as a full configuration interaction (FCI) method for small molecules, 7,10,[12][13][14] it was recognised that DMRG is best used to describe non-dynamical correlation in active spaces. The DMRG algorithm exhibits a cost scaling of O(k 3 …”

Hiking on the potential energy surface of a functional tyrosinase model – implications of singlet, broken-symmetry and triplet description

“…3 Moreover this equilibrium is theoretically regarded as a torture track for computational chemistry, 8,9 since the amount of exact exchange heavily influences the predicted energies for the O/P equilibrium. 9 Several studies with multi-reference (MR) calculations based on a wave functional theory (WFT) method such as CASPT2, 10 MRCI + Q, 11 DMRG, 12 and RASPT2 13 have been carried out with ammonia ligands as a substitution for histidine residues. However, the small model does not reproduce experimental Cu-Cu and O-O distances of ''real'' peroxo complexes.…”