Comprehensive ab initio calculation and simulation on the low-lying electronic states of TlX (X = F, Cl, Br, I, and At)

The low-lying electronic states of TlX (X=F, Cl, Br, I, and At) are investigated using the configuration interaction based complete active space third-order perturbation theory [CASPT3(CI)] with spin-orbit coupling accounted for. The potential energy curves and the corresponding spectroscopic constants are reported. The results are grossly in good agreement with the available experimental data. The absorption spectra are simulated as well to reassign the experimental bands. The present results are also useful for guiding future experimental measurements.     

Ab initio calculation of the electronic structure of the strontium hydride ion (SrH+)

The potentials, spectroscopic properties and electric dipole moments of SrH⁺ are computed for 63 molecular states dissociating up to Sr²⁺ + H^? using an ab initio approach. The ab initio formalism is based on large basis sets, nonempirical atomic pseudopotential for strontium core, correlation treatment for core valence through the effective core polarization potentials and for valence through full valence configuration interaction. Our theoretical molecular constants match published values very well and a large amount of new results is produced. Unusual potential shapes are found in ¹Σ⁺ states often caused by avoided crossing series between them and imprinted by the ionic state Sr²⁺H^?. The high potential energy curves suggest, it is possible to form H^? or at least to neutralize H⁺ in collisions with strontium. © 2014 Wiley Periodicals, Inc.     

Theoretical study of spectroscopic and molecular properties of several low‐lying electronic states of CO molecule

The potential energy curves (PECs) of eight low‐lying electronic states (X¹Σ⁺, a³Π, a′³Σ⁺, d³Δ, e³Σ^?, A¹Π, I¹Σ^?, and D¹Δ) of the carbon monoxide molecule have been studied by an ab initio quantum chemical method. The calculations have been performed using the complete active space self‐consistent field method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation‐consistent aug‐cc‐pV5Z basis set. The effects on the PECs by the core‐valence correlation and relativistic corrections are included. The way to consider the relativistic corrections is to use the third‐order Douglas–Kroll Hamiltonian approximation at the level of a cc‐pV5Z basis set. Core‐valence correlation corrections are performed using the cc‐pCVQZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are corrected for size‐extensivity errors by means of the Davidson modification (MRCI+Q). The spectroscopic parameters (D_e, T_e, R_e, ω_e, ω_ex_e, ω_ey_e, B_e, α_e, and γ_e) of these electronic states are calculated using these PECs. The spectroscopic parameters are compared with those reported in the literature. Using the Breit–Pauli operator, the spin–orbit coupling effect on the spectroscopic parameters is discussed for the a³Π electronic state. With the PECs obtained by the MRCI+Q/aug‐cc‐pV5Z+CV+DK calculations, the complete vibrational states of each electronic state have been determined. The vibrational manifolds have been calculated for each vibrational state of each electronic state. The vibrational level G(ν), inertial rotation constant B_ν, and centrifugal distortion constant D_ν of the first 20 vibrational states when the rotational quantum number J equals zero are reported and compared with the experimental data. Comparison with the measurements demonstrates that the present spectroscopic parameters and molecular constants determined by the MRCI+Q/aug‐cc‐pV5Z+CV+DK calculations are both reliable and accurate. © 2012 Wiley Periodicals, Inc.     

Theoretical study on the reaction CX3 + SiH(CH3)3 (X = H, F)

Theoretical investigations are carried out on the multiple-channel reactions, CH(3) + SiH(CH(3))(3) → products and CF(3) + SiH(CH(3))(3) → products. The minimum energy paths (MEP) are calculated at the MP2/6-311 + G(d,p) level, and energetic information is further refined by the MC-QCISD (single point) method. The rate constants for major reaction channels are calculated by the canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) correction over the temperature range 200-1500 K. The theoretical rate constants are in good agreement with the available experimental data and are found to be k(1a)(T) = 1.93 × 10(-24) T(3.15) exp(-1214.59/T) and k(2a)(T) = 1.33 × 10(-25) T(4.13) exp(-397.94/T) (in unit of cm(3) molecule(-1) s(-1)). Our calculations indicate that hydrogen abstraction channel from SiH group is the major channel due to the smaller barrier height among five channels considered.     

Theoretical study on the low-lying electronic states of NiH and NiAt

The low-lying electronic states of NiH and NiAt are investigated by using multireference second-order perturbation theory with relativistic effects taken into account. The potential energy curves as well as the corresponding spectroscopic constants are reported. The results are grossly in good agreement with the available experimental data and should thus be very useful for guiding future experimental measurements. A cross comparison with other nickel monohalides NiX (X = F, Cl, Br, and I) reveals that the change in the spin-orbit splittings when going from lighter to heavier ligands results more from the state interaction than from the relativistic effects of the ligands.     

Theoretical study and rate constants calculation for the reactions X + CF3CH2OCF3 (X = F,Cl, Br)

The multiple‐channel reactions X + CF₃CH₂OCF₃ (X = F, Cl, Br) are theoretically investigated. The minimum energy paths (MEP) are calculated at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD (single‐point) method. The rate constants for major reaction channels are calculated by canonical variational transition state theory (CVT) with small‐curvature tunneling (SCT) correction over the temperature range 200–2000 K. The theoretical three‐parameter expressions for the three channels k_1a(T) = 1.24 × 10^?15T^1.24exp(?304.81/T), k_2a(T) = 7.27 × 10^?15T^0.37exp(?630.69/T), and k_3a(T) = 2.84 × 10^?19T^2.51 exp(?2725.17/T) cm³ molecule^?1 s^?1 are given. Our calculations indicate that hydrogen abstraction channel is only feasible channel due to the smaller barrier height among five channels considered. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2012     

Theoretical study of low‐lying electronic states of the LiRb+ molecular ion: Structure,spectroscopy and transition dipole moments

The electronic structure and the spectroscopic properties for low‐lying electronic states of the LiRb⁺ molecular ion, dissociating into Li (2s, 2p, 3s, 3p, 3d, 4s, and 4p) + Rb⁺ and Li⁺ + Rb (5s, 5p, 4d, 6s, 6p, 5d, and 7s), have been investigated using an ab initio approach based on non‐empirical pseudo potentials for the Li and Rb cores and parametrized l‐dependent polarization potential. We have determined the adiabatic potential energy curves and their spectroscopic constants for many electronic states of ²Σ⁺, ²Π, and ²Δ symmetries. A satisfying agreement, for the spectroscopic constants, has been obtained for the ground and the first excited states with the available theoretical works. Potential energy curves were presented, for the first time, for the higher excited states. In addition, we have localised and analysed the avoided crossings between electronic states of ²Σ⁺ and ²Π symmetries. Their existences can be related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Li⁺Rb and LiRb⁺. Moreover, we have determined the transition dipole moments from X²Σ⁺ and 2²Σ⁺ states to higher excited states of ²Σ⁺ and ²Π symmetries. For our best knowledge, no experimental data on the LiRb⁺ molecular ion is available. These theoretical data can help experimentalists to optimize photoassociative formation of ultracold LiRb⁺ molecular ion and their longevity in a trap or in an optical lattice. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Spectroscopic constants and molecular properties of the X2Π and a4Σ− electronic states of the SiF radical

The potential energy curves (PECs) of the X²Π and a⁴Σ^? electronic states of the SiF radical have been studied by an ab initio quantum chemical method. The calculations have been made using the complete active space self‐consistent field (CASSCF) method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with several correlation‐consistent basis sets. The effects on the PECs by the core‐valence correlation and relativistic corrections are included. The way to consider the relativistic correction is to use the third‐order Douglas–Kroll Hamiltonian approximation. The relativistic corrections are made at the level of cc‐pV5Z basis set. The core‐valence correlation corrections are performed using the cc‐pCV5Z basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size‐extensivity errors by means of the Davidson modification (MRCI+Q). These PECs are extrapolated to the complete basis set limit by the total‐energy extrapolation scheme. Using these PECs, the spectroscopic parameters are determined and compared with those reported in the literature. With these PECs obtained by the MRCI+Q/CV+DK+56 calculations, the vibrational levels, inertial rotation, and centrifugal distortion constants of the first 20 vibrational state of each electronic state are calculated when the rotational quantum number J equals zero. Comparison with the Rydberg‐Klein‐Rees (RKR) data shows that the present results are reliable and accurate. The molecular constants of the X²Π and a⁴Σ^? electronic states determined by the MRCI+Q/CV+DK+56 calculations should be good prediction for future laboratory experiment. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical investigation of the structural,elastic, electronic and optical properties of the ternary indium sulfide layered structures AInS2 (A = K,Rb and Cs)

Ab initio calculations were performed to investigate the structural, elastic, electronic and optical properties of the ternary layered systems AInS₂ (A = K, Rb and Cs). The calculated structural parameters are in good agreement with the existing experimental data. Analysis of the electronic band structure shows that the three studied materials are direct band-gap semiconductors. Density of states, charge transfers and charge density distribution maps were computed and analyzed. Numerical estimations of the elastic moduli and their related properties for single-crystal and polycrystalline aggregates were predicted. The optical properties were calculated for incident radiation polarized along the [100], [010] and [001] crystallographic directions. The studied materials exhibit a noticeable anisotropic behaviour in the elastic and optical properties, which is expected due to the symmetry and the layered nature of these compounds.     

The structure of CX2YNO (X, Y=F, Cl) molecules in the ground and lowest excited singlet electronic states

Ab initio quantum-chemical calculations of equilibrium geometric parameters, vibrational frequencies, and potentials of internal rotation for CCIF₂NO and CCl₂FNO molecules in the ground (S₀) and lowest excited singlet (S₁) electronic states were performed. The results of calculations were compared with experimental data. A new interpretation of experimental spectra of the CCIF₂NO molecule was suggested. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1453–1458, August, 1999.     

Electron affinities of heavier phosphoryl and thiophosphoryl halides APX3 (A = O, S and X = Br, I)

We carried out computational studies of OPX₃ and SPX₃ (X = Br and I) molecules and their corresponding anions using density functional theory, Møller‐Plesset, and CCSD(T) methods with newly developed model core potentials (MCP). Reliabilities of the MCP were demonstrated by comparing experimental and calculated results. We computed the geometric structure, electron affinities, and electrostatic moments using systematic sequences of the dzp‐, tzp‐, and qzp‐quality basis sets. Both C_3v and C_s symmetries were assumed to ascertain that minima on the potential energy surface were found. Infrared and Raman frequencies were calculated and compared with available experimental data. Natural population analyses were performed and used to determine distribution of the extra electron in anions. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007     

The effect of the iterative triple and quadruple cluster amplitudes on the adiabatic potential curve in the coupled cluster calculations of the ground electronic state of the Yb dimer

The dissociation energy, equilibrium internuclear distance, and spectroscopic constants for the ¹Σ ground state of the Yb₂ molecule are calculated. The relativistic effects are introduced through generalized relativistic effective core potentials with very high precision. The scalar relativistic coupled cluster method particularly well suited for closed‐shell van der Waals systems is used for the correlation treatment. Extensive generalized correlation basis sets were constructed and used. The relatively small corrections for high‐order cluster amplitudes and spin—orbit interactions are taken into account using smaller basis sets and the spin—orbit density functional theory. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study of atoms by the electronic kinetic energy density and stress tensor density

The electronic structure of atoms in the first, second, and third periods were analyzed using the electronic kinetic energy density and stress tensor density, which are local quantities motivated by quantum field theoretic consideration, specifically the rigged quantum electrodynamics. The zero surfaces of the electronic kinetic energy density, which are called as the electronic interfaces, of the atoms were computed. It was found that their sizes exhibited clear periodicity and were comparable to the conventional atomic and ionic radii. The electronic stress tensor density and its divergence, tension density, of the atoms, were also computed and how their electronic structures were characterized by them was discussed. © 2016 Wiley Periodicals, Inc.     

HCCO自由基与LiX(X=F,Cl,Br)锂键复合物的从头算研究

在MP2/6-311++G**水平上优化乙烯酮自由基与LiX(X=F,Cl,Br)形成锂键复合物.当卤素的电负性很强(如F元素),使得Li原子处于缺电子状态,此时,电子给体会把电子偏移向锂,形成共价性较强的锂键.而当卤素的电负性减弱时,锂键中主要成分逐渐变为离子键,并且此时锂键性质还要受电子给体影响.另外,由于HCCO为缺电子结构,电负性较弱且体积较大的卤素中的孤对电子会与HCCO之间通过静电相互作用,使得HCCO…Li—X键夹角变小,接近120°.锂键性质对HCCO…LiX(X=F,Cl,Br)复合物中Li—X的伸缩振动频率有直接影响.当锂键表现为共价性时,该频率红移,而当锂键表现为离子性时,该频率蓝移.但是,由于Cl的电负性与O的接近,C的电负性与Br接近所以,在O…Li…Cl和C…Li…Br中容易形成共振结构,导致远大于在其他复合物中的红移.     

Synthesis,Crystal Structure,and Vibrational Spectroscopy of the Alkali Diselenates A2Se2O7 (A = Li – Cs)

The reaction of alkali carbonates and selenium acid yielded the “pyroanions” [Se₂O₇]^2– containing alkali diselenates. By varying the alkali carbonates we were able to synthesize and determinate the crystal structures of the whole row from Li to Cs. Li₂Se₂O₇ crystallizes isotypic to Li₂S₂O₇ [Pnma, Z = 4, a = 13.815(3), b = 8.452(2) c = 5.0585(10) Å]. The structure of Na₂Se₂O₇ [P$\bar{1}$ , Z = 2, a = 6.9896(14), b = 6.9938(14), c = 7.0829(14) Å, α = 83.32(3), β = 64.56(3), γ = 83.18(3)°] is isotypic to Ag₂S₂O₇. A₂Se₂O₇ (A = K, Rb) [A = K: C2/c, Z = 4, a = 12.851(3), b = 7.5677(15), c = 7.5677(15) Å, β = 93.35(3)°; A = Rb: C2/c, Z = 4, a = 13.118(3), b = 7.7963(16), c = 7.7811(16) Å, β = 94.03(3)°] are isotypic to K₂S₂O₇. The crystal structure of Cs₂Se₂O₇ [P$\bar{1}$ , Z = 10, a = 7.7271(3), b = 16.2408(8), c = 18.4427(8) Å, α = 89.685(2), β = 89.193(2), γ = 76.251(2)°] seems to be isotypic to the averaged room‐temperature modification of Cs₂S₂O₇. With exception of the caesium compound all diselenate anions show an ecliptic arrangement and can be therefore classified as dichromate‐like structures. In Cs₂Se₂O₇ most of the [Se₂O₇]^2– units have a staggered alignment. The transition between both orientations can be explained by the increase of the cations size. Additionally the vibrational spectra of A₂Se₂O₇ with A = Li – Cs are discussed as well as the resulting bond forces.     

Electronic structure and properties of isoelectronic magic clusters: Al13X (X=H,Au,Li,Na,K,Rb,Cs)

The equilibrium structure, stability, and electronic properties of the Al(13)X (X=H,Au,Li,Na,K,Rb,Cs) clusters have been studied using a combination of photoelectron spectroscopy experiment and density functional theory. All these clusters constitute 40 electron systems with 39 electrons contributed by the 13 Al atoms and 1 electron contributed by each of the X (X=H,Au,Li,Na,K,Rb,Cs) atom. A systematic study allows us to investigate whether all electrons contributed by the X atoms are alike and whether the structure, stability, and properties of all the magic clusters are similar. Furthermore, quantitative agreement between the calculated and the measured electron affinities and vertical detachment energies enable us to identify the ground state geometries of these clusters both in neutral and anionic configurations.     

Local density functional study of the structural and electronic properties of C60 and XC60 (X=K, Rb, Cs)

Results of first principles local density total energy and atomic force calculations carried out for free C₆₀ and XC₆₀ (X=K, Rb, Cs) molecular clusters are reported. The optimization of the geometry results in the bond lengths between adjacent carbon atoms being 1.387 and 1.445 Å, which are in very good agreement with the latest X-ray diffraction values. Energy levels, charge distributions, and wavefunction characteristics are obtained and discussed. The results for C₆₀ are in very good agreement with recently measured photoemission energy distribution curves (EDC) for the valence band states. The highest occupied molecular orbitals (HOMO) are found to be fully occupied H_u states and are 1.7 eV below the lowest unoccupied molecular orbitals (LUMO) which are of T_1u symmetry. Similar results obtained for the XC₆₀ clusters show that rigid-band-like behavior is found in the electronic structures after putting an alkali atom at the center of a C₆₀ ball. In each case, the alkali atom is almost fully ionized with the transferred electron distributed over the surface shell of C₆₀; the center region of the ball has very low charge density.     

The Low and High Temperature Crystal Structures of [Mg(H2O)6]XBr3 Double Salts (X = Rb,Cs

The crystal structures of the alkali double salts [Mg(H₂O)₆]XBr₃ (X = Rb⁺, Cs⁺) were analyzed in dependence on temperature from laboratory and synchrotron X‐ray powder diffraction data. At room temperature, both compounds are isostructural to [Mg(H₂O)₆](NH₄)Br₃ (C2/c; Z = 4; a = 9.64128(6) Å, b = 9.86531(5) Å, c = 13.78613(9) Å, β = 90.0875(5)° for [Mg(H₂O)₆]RbBr₃; a = 9.82304(7) Å, b = 9.98043(6) Å, c = 14.0100(1) Å, β = 90.1430(4)° for [Mg(H₂O)₆]CsBr₃). At a temperature of T = 358 K, [Mg(H₂O)₆]RbBr₃ undergoes a reversible phase transition towards a cubic perovskite type of structure with the [Mg(H₂O)₆]²⁺ octahedron in the cuboctahedral cavity exhibiting 4‐fold disorder ( ; a = 6.94198(1) Å at T = 458 K). In case of [Mg(H₂O)₆]CsBr₃ the lattice parameters in dependence on temperature show a distinct kink at T = 340 K, but no symmetry breaking phase transition occurs before decomposition starts. The dominant role of hydrogen bonding with respect to the stability of the crystal structures is discussed.     

Generalized relativistic effective core potential calculations of the adiabatic potential curve and spectroscopic constants for the ground electronic state of the Ca2 molecule

The potential curve, dissociation energy, equilibrium internuclear distance, and spectroscopic constants for the ground state of the Ca₂ molecule are calculated with the help of the generalized relativistic effective core potential method, which allows one to exclude the inner core electrons from the calculations and to take the relativistic effects into account effectively. Extensive generalized correlation basis sets were constructed and used. The scalar relativistic coupled cluster method with corrections for high‐order cluster amplitudes is used for the correlation treatment. The results are analyzed and compared with the experimental data and corresponding all‐electron results. © 2013 Wiley Periodicals, Inc.     

Density functional studies of AnF6 (An=U,Np, and Pu) and UF6−nCln (n=1–6) using hybrid functionals: geometries and vibrational frequencies

We have compared the performance of widely used hybrid functionals for calculating the bond lengths and harmonic vibrational frequencies of AnF₆ (An=U, Np, and Pu) and UF_6?nCl_n (n=1–6) molecules using “small‐core” relativistic effective core potentials and extended basis sets. The calculated spectroscopic constants compare favorably with experimental data for the bond lengths (average error ≤ 0.01 Å) and vibrational frequencies (average error ≤ 7 cm^?1) of the AnF₆ molecules. The experimental vibrational frequencies of the stretching modes were available for most of the UF_6?nCl_n (n=1–6) molecules. The calculated vibrational frequencies are in good agreement with the experimental data to within 4.6 cm^?1 and 7.6 cm^?1 for selected Becke1 and Lee, Yang, Parr (B1LYP), and Becke3 and Perdew, Wang (B3PW91) functionals, respectively. We conclude that one can predict reliable geometries and vibrational frequencies for the unknown related systems using hybrid density functional calculations with the RECPs. The geometries and vibrational frequencies of the UF_6?nCl_n (n=1–6) molecules that have not been determined experimentally are also presented and discussed. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 2010–2017, 2001