### Abstract

We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as a basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys.2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insight into chemically interesting features of the molecule under study such as the distribution of α and β electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches [J. Chem. Theory Comput.2011, 7, 2740].

Original language | English |
---|---|

Pages (from-to) | 1970-1982 |

Number of pages | 13 |

Journal | Journal of Chemical Theory and Computation |

Volume | 8 |

Issue number | 6 |

DOIs | |

Publication status | Published - Jun 12 2012 |

### Fingerprint

### ASJC Scopus subject areas

- Physical and Theoretical Chemistry
- Computer Science Applications

### Cite this

*Journal of Chemical Theory and Computation*,

*8*(6), 1970-1982. https://doi.org/10.1021/ct300211j

**Accurate ab initio spin densities.** / Boguslawski, Katharina; Marti, Konrad H.; Legeza, O.; Reiher, Markus.

Research output: Contribution to journal › Article

*Journal of Chemical Theory and Computation*, vol. 8, no. 6, pp. 1970-1982. https://doi.org/10.1021/ct300211j

}

TY - JOUR

T1 - Accurate ab initio spin densities

AU - Boguslawski, Katharina

AU - Marti, Konrad H.

AU - Legeza, O.

AU - Reiher, Markus

PY - 2012/6/12

Y1 - 2012/6/12

N2 - We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as a basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys.2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insight into chemically interesting features of the molecule under study such as the distribution of α and β electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches [J. Chem. Theory Comput.2011, 7, 2740].

AB - We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as a basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys.2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insight into chemically interesting features of the molecule under study such as the distribution of α and β electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches [J. Chem. Theory Comput.2011, 7, 2740].

UR - http://www.scopus.com/inward/record.url?scp=84862168283&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84862168283&partnerID=8YFLogxK

U2 - 10.1021/ct300211j

DO - 10.1021/ct300211j

M3 - Article

AN - SCOPUS:84862168283

VL - 8

SP - 1970

EP - 1982

JO - Journal of Chemical Theory and Computation

JF - Journal of Chemical Theory and Computation

SN - 1549-9618

IS - 6

ER -