Hartree–Fock calculation of the electronic structure of a Cu+ impurity in NaCl

We study correlations between Madelung constants, charges of surface ions, and chemical activity of low-coordinated sites of the MgO crystal surface with respect to dissociative adsorption of hydrogen. The ab initio Embedded Cluster model [Puchin et al., Phys. Rev. B 47, 6226 (1993)] employed in this study allowed us to reproduce correctly both short range and long range (Madelung) parts of the interaction between ions in a quantum cluster and the rest of the crystal. Our results show that sites having the same coordination numbers may have different properties, depending on values of Madelung constants. Lower Madelung constants correspond to lower ionicity, higher energy of H2 adsorption, stronger O–H and Mg–H bonds, and larger spatial separation of two adsorbed hydrogen atoms.

Section: Theoretical Methodsmentioning

confidence: 99%

Correlation between the Madelung field and the reactivity of the MgO low-coordinated surface sites

Stefanovich

Truong

1995

“…For highly ionic crystals this difficulty can be overcome by using effective core pseudopotentials to describe interaction of ions in the buffer zone with cluster electrons. 21,22 For semiconductors and zeolites, one may use pseudoatoms to cap bonds at the boundary of the QM cluster. 20 Classical particles in the buffer zone can interact with each other and with cluster nuclei by means of force fields.…”

Section: Methodsmentioning

confidence: 99%

A theoretical approach for modeling reactivity at solid–liquid interfaces

Stefanovich

Truong

1997

Determining the distribution of silicon monofluoride on hydrofluoric acid-treated Si (111) surface by exchange reaction with molecules at the solid/liquid interface Appl.We present a new general methodology capable of modeling chemical reactions at solid-liquid interfaces called CECILIA ͑combined embedded cluster at the interface with liquid approach͒. The main idea is to combine the embedded cluster molecular orbital or density functional methods for describing interactions at the surface of a solid with the dielectric continuum approach for modeling a liquid. More details are given on how to apply this methodology to model processes at the ionic solid-water interface. Geometries and adsorption binding energies of H 2 O, NaCl, Na ϩ , and Cl Ϫ at the NaCl͑001͒-water interface are calculated using this approach and compared with those at the NaCl͑001͒-vacuum interface.

“…This approach has been used extensively in embedded cluster calculations. [24][25][26][27] An example of one of the clusters considered in these calculations surrounded by the set of PPs is shown in Fig. 1.…”

Section: Model Systemsmentioning

confidence: 99%

Rotationally invariant ab initio evaluation of Coulomb and exchange parameters for DFT+U calculations

Mosey

Liao

Carter

2008

339

316

Conventional density functional theory (DFT) fails for strongly correlated electron systems due to large intra-atomic self-interaction errors. The DFT+U method provides a means of overcoming these errors through the use of a parametrized potential that employs an exact treatment of quantum mechanical exchange interactions. The parameters that enter into this potential correspond to the spherically averaged intra-atomic Coulomb (U) and exchange (J) interactions. Recently, we developed an ab initio approach for evaluating these parameters on the basis of unrestricted Hartree-Fock (UHF) theory, which has the advantage of being free of self-interaction errors and does not require experimental input [Mosey and Carter, Phys. Rev. B 76, 155123 (2007)]. In this work, we build on that method to develop a more robust and convenient ab initio approach for evaluating U and J. The new technique employs a relationship between U and J and the Coulomb and exchange integrals evaluated using the entire set of UHF molecular orbitals (MOs) for the system. Employing the entire set of UHF MOs renders the method rotationally invariant and eliminates the difficulty in selecting unambiguously the MOs that correspond to localized states. These aspects overcome two significant deficiencies of our earlier method. The new technique is used to evaluate U and J for Cr(2)O(3), FeO, and Fe(2)O(3). The resulting values of U-J are close to empirical estimates of this quantity for each of these materials and are also similar to results of constrained DFT calculations. DFT+U calculations using the ab initio parameters yield results that are in good agreement with experiment. As such, this method offers a means of performing accurate and fully predictive DFT+U calculations of strongly correlated electron materials.