Dingguo Dai

Electronic structures of Pd4 and Pt4

Complete active space multiconfiguration self‐consistent field (CAS‐MCSCF) followed by multireference configuration interaction computations which included up to 4.1 million configurations and correlated all 40 electrons of Pd4 and Pt4 were made. Relativistic effective core potentials (RECPS) were employed for both Pt and Pd atoms. We found 44 electronic states for Pd4 within the 2.2 eV region and 51 electronic states for Pt4 within 1.2 eV. Two nearly‐degenerate electronic states with tetrahedral geometries were found as candidates for the ground states of Pd4 and Pt4 with 3T1 and 1A1 symmetries at the highest level of theory. The metal–metal bond lengths for Pd4 and Pt4 were found to be 2.686 and 2.602 A for the 3T1 state and 2.696 and 2.595 A for the 1A1 state, respectively. The atomization energies of Pd4 and Pt4 were computed as 5.63 and 11.8 eV, respectively, suggesting that Pt4 is considerably more bound compared to Pd4. Relativistic effects are attributed to the enhanced stability of Pt4. The Mulli...

Electronic structure of group IV tetramers (Si4–Pb4)

Geometries and energy separations of ten electronic states of Ge4, Sn4, and Pb4 are computed and compared with Si4. We employ complete active space multiconfiguration self‐consistent‐field followed by multireference singles + doubles configuration interaction calculations. The ground states of Ge4–Pb4 are found to be 1Ag states with equilibrium geometries of rhombus similar to Si4. Relativistic effects are found to be significant for Pb4. Atomization/dissociation energies of Ge4–Pb4 are computed and compared with Si4. Pb4 was found to be considerably less bound compared to other tetramers. The energy separations of the excited electronic states were found to decrease, especially the splitting between the rhombus and tetrahedral structures, as one goes down the group.

Group V trimers and their positive ions: The electronic structure and potential energy surfaces

Complete active space multiconfiguration self‐consistent field (CAS‐MCSCF) followed by multireference configuration interactions (MRCI) calculations are made on the electronic states of P3, As3, Sb3, Bi3 and all their positive ions. All group V trimers have Jahn‐Teller distorted 2A2 ground states arising from the 2E‘(D3h) state while the positive ions have 1A’1(D3h) equilateral‐triangular ground states. For the neutral species, the 2B1 Jahn‐Teller component was found to be nearly degenerate with the 2A2 component. Extensive studies on As3, Sb3, and Bi3 reveal the existence of 4A2, 4E’, and 2E’ (D3h) excited states which also undergo Jahn‐Teller distortion. The binding energies and the ionization potentials (IP) of all group V trimers were computed and compared with known experimental data on some of these species. The IPs and the binding energies per atom of group V trimers were found to be significantly smaller than dimers thus exhibiting odd–even alternation in these properties. Our computations explain...

Electronic states of Yn (n=2–4)

We compute the geometries and energy separations of several electronic states of Yn (n=2–4). The complete‐active‐space self‐consistent‐field (CASSCF) followed by multireference singles+doubles configuration interaction (MRSDCI) calculations which included up to 2.6 million configurations are made in this study. We find two nearly degenerate states, namely, 3T1 and 1A1 of tetrahedral geometry, as candidates for the ground state of Y4. The Y–Y bond lengths are computed as 3.41 and 3.42 A for 3T1 and 1A1 states, respectively. The electronic states with the rhombus structures are found to be ≥0.34 eV above the tetrahedral ground state for Y4. We found two nearly degenerate electronic states with D3h geometries as candidates for the ground state of Y3 (2A‘2 and 2A’1). Two electronic states of Y2, namely, 5Σu− and 1Σg+ (short R) are also studied.

Electronic states of the Ga3As2 and Ga2As3 clusters

Abstract We computed the optimized geometries and energy separations of several electronic states of Ga 3 As 2 and Ga 2 As 3 clusters using the complete active space multiconfiguration self-consistent-field (CASSCF) followed by multireference singles + doubles configuration interaction (MRSDCI) computations which included up to 1.9 million configurations. The properties of the electronic states in distorted and undistorted trigonal bipyramid, and edge-capped tetrahedron structures of Ga 3 As 2 are computed. Two nearly degenerate structures and several excited states were found for Ga 3 As 2 while the Ga 2 As 3 cluster exhibits undistorted trigonal bipyramidal states.

Geometries and energies of electronic states of AsH3, SbH3, and BiH3 and their positive ions

Geometries, potential energy surfaces, bond energies, dipole moments, ionization potentials and other properties of MH3 and MH+3 species (M=As, Sb and Bi) are obtained using complete active space self‐consistent field (CASSCF) followed by full second‐order configuration interaction (SOCI) and relativistic configuration interaction (RCI) methods. Potential energy surfaces of six electronic states of AsH3 and SbH3 and three states of BiH3 are obtained. The ground states of MH3 species are found to be of Xu20091A1 symmetries (C3v) with pyramidal geometries. The geometrical and other parameters of MH3 species are AsH3[re=1.517 A, θe=92.2°, D(H2As–H)=74.6 kcal/mol, IP=9.5 eV], SbH3[re=1.719u2009A, θe=91.5°, D(H2Sb–H)=63.3 kcal/mol, IP=8.9 eV], BiH3[re=1.865 A, θe=90.3°, D(H2Bi–H)=51.8 kcal/mol, IP=9.0 eV]. The equilibrium geometries of MH+3 ions are found to be close to planar. For AsH3 the agreement in IP and bond energy between the present theoretical results and the experimental values obtained recently by Berkowit...

Eight electronic states and potential energy surfaces of Ge3

Abstract Complete active space multiconfiguration self-consistent field followed by multireference singles+doubles configuration interaction calculations are made on eight electronic states of Ge 3 . We compute the entire bending potential energy surfaces of these states. We find two nearly degenerate states ( 1 A 1 , 3 B 2 ) as candidates for the ground state of Ge 3 . Six excited electronic states within ≈ 1 eV of the ground state are also found.

Pt3Au and PtAu clusters: Electronic states and potential energy surfaces

We carried out complete active space multiconfiguration self‐consistent‐field calculations followed by multireference singles+doubles configuration interaction with the Davidson correction which included up to 3.55 million configurations employing relativistic effective core potentials on Pt3+Au and PtAu clusters. Four low‐lying electronic states were identified for Pt3+Au. The 2A2 electronic state (C3v) was found to be the ground state of Pt3Au. Spin–orbit effects were found to be significant. We also computed six low‐lying electronic states of PtAu and four low‐lying electronic states of PtAu+. The 5/2 (2Δ) and 0+(1Σ+) states were found to be the ground states of PtAu and PtAu+, respectively.

High-spin electronic states of the rhodium trimer (Rh3)

Abstract Ab initio studies employing complete active space multi-configuration self-consistent field followed by large-scale multi-reference configuration interaction calculations which included more than 3 million configurations on high-spin sextet, octet, decret and low-spin doublet states of rhodium trimer (Rh3) are carried out. Our computations yield three nearly degenerate sextet states as candidates for the ground state confirming the recent ESR spectra of Rh3 which have revealed that the ground state of Rh3 has S = 5 2 . The geometries of all high-spin sextet and octet states are very acute isosceles triangles. The Mulliken population analyses confirm the ESR spectral inference that the unpaired electrons reside on the 4d orbitals of Rh atoms.

Potential energy surfaces for Pt3+H2 and Pd3+H2 systems

Potential energy surfaces of Pt3+H2 and Pd3+H2 systems are computed for different modes of approach using the complete active space multiconfiguration self‐consistent field theory (CAS‐MCSCF). The equilibrium geometries and the dissociation limits were computed using multireference singles+doubles configuration method which included up to 1.54 million configurations. For both in‐plane and out‐of‐plane approaches barriers arise from the crossing of the Pt3+H+H (or Pd3+H+H) surface and the Pt3+H2 (or Pd3+H2) surface. Three potential minima were found in the in‐plane potential energy surface in the post‐barrier region. One of these minima exhibited two Pt–H–Pt (or Pd–H–Pd) bridge bonds. For Pd3H2 this structure was found to be stable while for Pt3H2 two nearly degenerate structures were found as candidates for the ground state. The barrier for H2 dissociation in the out‐of‐plane approach was found to be larger and the out‐of‐plane minimum was higher in energy compared to the in‐plane minimum for both Pt3H2 a...