# Density functional theory with fractional orbital occupations.

@article{Chai2012DensityFT, title={Density functional theory with fractional orbital occupations.}, author={Jeng-Da Chai}, journal={The Journal of chemical physics}, year={2012}, volume={136 15}, pages={ 154104 } }

In contrast to the original Kohn-Sham (KS) formalism, we propose a density functional theory (DFT) with fractional orbital occupations for the study of ground states of many-electron systems, wherein strong static correlation is shown to be described. Even at the simplest level represented by the local density approximation (LDA), our resulting DFT-LDA is shown to improve upon KS-LDA for multi-reference systems, such as dissociation of H(2) and N(2), and twisted ethylene, while performing…

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## References

SHOWING 1-10 OF 189 REFERENCES

### Semiempirical hybrid density functional with perturbative second-order correlation.

- ChemistryThe Journal of chemical physics
- 2006

The uniformity with which B2-PLYP improves for a wide range of chemical systems emphasizes the need of (virtual) orbital-dependent terms that describe nonlocal electron correlation in accurate exchange-correlation functionals.

### SIMULATION OF NONDYNAMICAL CORRELATION IN DENSITY FUNCTIONAL CALCULATIONS BY THE OPTIMIZED FRACTIONAL ORBITAL OCCUPATION APPROACH : APPLICATION TO THE POTENTIAL ENERGY SURFACES OF O3 AND SO2

- Chemistry
- 1996

If the energies of occupied and empty orbitals as functions of N geometric parameters vary in different manners, single determinantal approaches such as the density functional ones may violate the…

### Diradicaloids: Description by the Spin-Restricted, Ensemble-Referenced Kohn-Sham Density Functional Method

- Chemistry
- 2000

A Kohn−Sham-type computational scheme capable of treating systems with strong nondynamic correlation is presented. The scheme, dubbed the spin-restricted, ensemble-referenced Kohn−Sham (REKS) method,…

### One - determinantal pure state versus ensemble Kohn-Sham solutions in the case of strong electron correlation: CH2 and C2

- Chemistry
- 1998

Abstract. The possibility that the Kohn-Sham (KS) solution for a noninteracting auxiliary electron system is not the conventional one-determinantal pure state but a few-determinantal ensemble has…

### Singlet-triplet energy gaps for diradicals from fractional-spin density-functional theory.

- Chemistry, PhysicsThe journal of physical chemistry. A
- 2011

A theoretical foray for using single-reference closed-shell ground states to describe diradicals by fractional-spin DFT (FS-DFT), which allows direct, self-consistent calculation of electronic properties using the electron density corresponding to the proper spin eigenfunction.

### Some Fundamental Issues in Ground-State Density Functional Theory: A Guide for the Perplexed.

- PhysicsJournal of chemical theory and computation
- 2009

Some fundamental issues in ground-state density functional theory are discussed without equations: (1) The standard Hohenberg-Kohn and Kohn-Sham theorems were proven for a Hamiltonian that is not…

### A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu.

- ChemistryThe Journal of chemical physics
- 2010

The revised DFT-D method is proposed as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.

### Density-functional approaches to noncovalent interactions: a comparison of dispersion corrections (DFT-D), exchange-hole dipole moment (XDM) theory, and specialized functionals.

- ChemistryThe Journal of chemical physics
- 2011

It is concluded that distinct, often contrasting, groups of these elicit the best performance within the accessible double-ζ or robust triple-η basis set regimes and among hydrogen-bonded or dispersion-dominated complexes.

### Density Functionals for Coulomb Systems

- Physics
- 1983

The idea of trying to represent the ground state (and perhaps some of the excited states as well) of atomic, molecular, and solid state systems in terms of the diagonal part of the one-body reduced…

### Generalized Gradient Approximation Made Simple.

- ChemistryPhysical review letters
- 1996

A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.