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- Rajendra R Zope, Brett I Dunlap
- The Journal of chemical physics
- 2006

Our recent formulation of the analytic and variational Slater-Roothaan (SR) method, which uses Gaussian basis sets to variationally express the molecular orbitals, electron density, and the one-body effective potential of density-functional theory, is reviewed. Variational fitting can be extended to the resolution of identity method, where variationality… (More)

- Igor V Schweigert, Brett I Dunlap
- The Journal of chemical physics
- 2009

Decomposition of energetic molecules such as pentaerythritol tetranitrate is accompanied by extensive changes in their electronic configuration and thus is challenging for ab initio Born-Oppenheimer molecular dynamics simulations. The performance of single-determinant methods (in particular, density-functional theory) is validated on electronic structure… (More)

- Brett I. Dunlap
- Computer Physics Communications
- 2005

- Yi Wang, Melanie Moses-DeBusk, +6 authors Bryan Eichhorn
- Journal of the American Chemical Society
- 2017

K5Sb4 and K3Sb7 Zintl ion precursors react with Pd(PPh3)4 in ethylenediamine/toluene/PBu4+ solutions to give crystals of Sb@Pd12@Sb20n-/PBu4+ salts, where n = 3, 4. The clusters are structurally identical in the two charge states, with nearly perfect Ih point symmetry, and can be viewed as an Sb@Pd12 icosahedron centered inside of an Sb20 dodecahedron. The… (More)

- Brett I Dunlap, Igor V Schweigert
- The Journal of chemical physics
- 2011

Variational fitting gives a stationary linear-combination of atomic potentials (LCAP) approximation to the Kohn-Sham (KS) potential, V. That potential is central to density-functional theory because it generates all orbitals, occupied as well as virtual. Perturbation theory links two self-consistent field (SCF) calculations that differ by the perturbation.… (More)

- Mark C Palenik, Brett I Dunlap
- The Journal of chemical physics
- 2015

Despite the fundamental importance of electron density in density functional theory, perturbations are still usually dealt with using Hartree-Fock-like orbital equations known as coupled-perturbed Kohn-Sham (CPKS). As an alternative, we develop a perturbation theory that solves for the perturbed density directly, removing the need for CPKS. This replaces… (More)

- Igor V Schweigert, Brett I Dunlap
- The Journal of chemical physics
- 2011

We present ab initio molecular dynamics simulations of head-on collisions between ethyl nitrate molecules at collisional energies from 200 to 1200 kJ/mol. Above a threshold energy, an increasing fraction of the collisions led to rapid dissociation on impact--"shattering." The probability of the shattering dissociation was derived from the quasiclassical… (More)

- Kah Chun Lau, Brett I Dunlap
- Journal of physics. Condensed matter : an…
- 2011

An empirically fitted atomic potential allows a classical molecular dynamics study of the static and dynamic properties of both crystalline and amorphous yttria-stabilized zirconia (YSZ) with typical dilute Y(2)O(3) concentrations (i.e. 3.0-12.0 mol% Y(2)O(3)) in the temperature range 300-1400 K. Based on the rigid ion model approximation, we find,… (More)

- Brett I Dunlap, Shashi P Karna, Rajendra R Zope
- The Journal of chemical physics
- 2006

Molecular dipole moments of analytic density-functional theory are investigated. The effect of element-dependent exchange potentials on these moments are examined by comparison with conventional quantum-chemical methods and experiment for the subset of the extended G2 set of molecules that have nonzero dipole moment. Fitting the Kohn-Sham [Phys. Rev. 140,… (More)

- Kah Chun Lau, Brett I Dunlap
- Journal of physics. Condensed matter : an…
- 2009

A study of lattice dielectric and thermodynamic properties of yttria stabilized zirconia (YSZ) crystals as a function of yttria concentration is reported. This study is based on density functional perturbation theory, using ABINIT. Within the local density approximation and the harmonic approximation, we find excellent agreement between calculated and low… (More)