State-specific multireference complete-active-space coupled-cluster approach versus other quantum chemical methods: dissociation of the N2 molecule

A comprehensive comparison of different quantum-chemical methods applied to calculate the N₂ ground state potential energy curve is presented. In the comparison we highlight the multireference state-specific (MRSS) coupled-cluster (CC) approach with the complete-active-space (CAS) reference and with single and double excitations from all reference determinants in the CC operator developed in our group. The method is called CASCCSD. The energy and amplitude equations for the method and the corresponding computer code have been generated using a computerized automative procedure that in the present work was extended to produce a parallel computer code. The complete CASCCSD wave function for N₂ includes some selected eight-fold excitations in the CC operator. An analysis of the wave function estimates the importance of those excitations at large internuclear separations.     

Composition and kinetic characteristics of vapour phase during mercuric iodide growing

The results of thermodynamical analysis of the vapour phase are presented for mostly often used growth conditions. It is shown that the vapour phase may contain: HgI₂(g), Hg(g), I₂(g), I(g). However, the degree of decomposition does not exceed one percent. Moverover, the following dependences are calculated and presented in a graphic form for HgI₂ + I₂ vapour mixture: the coefficient of dynamic viscosity from composition and temperature; the coefficient of diffusion with temperature and pressure; the coefficient of heat conductivity from composition and temperature.     

Study of radiative and convective heat transfer when a radiating mixture of carbon dioxide and nitrogen flows past the critical point of a body

The results are given of an investigation of the convective and radiative heat transfer at the leading critical point of a body in the flow of a radiating mixture of carbon dioxide and nitrogen, taking account of viscosity and thermal conductivity. The system of equations is written down under the assumption that the shock layer is thin, and its solution is obtained in the region between the body and the shock wave. It is assumed that there is local thermodynamic equilibrium throughout the compressed layer. The coefficients of absorption of the mixture are assumed to depend on the wavelength, the temperature, and the pressure. From the solution we determine the radiative and convective thermal fluxes at the wall, taking account of their interaction for temperatures behind the shock wave of 9000–12000 deg K and pressures of p=1 and 10 atm. By analyzing these results it is concluded that the effect of radiation on the convective heat transfer is insignificant, the effect being qualitatively different at large and small pressures. The fundamental contributions to the radiant thermal flux at the wall in the versions of the problem considered come from the following spectral interval: 0.128–0.33, where there is a fourth positive system of carbon monoxide bands (~43%), and 0.33–0.66, where there is an ultraviolet system of cyanogen (~40%). The contribution from the spectral interval 0.80–1.15 is ~20%. Only about 15% of the radiant energy comes from the comparatively large interval 0.45–0.80. As the pressure increases, the contribution from the ultraviolet part of the spectrum falls, and the contribution from the visible part of the spectrum increases.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 39–47, March–April, 1971.     

Preliminary characterization of semiconductor detectors in the soft X-ray range using synchrotron radiation from the VEPP-4 storage ring

A photodiode developed at the Ioffe Physico-Tech nical Institute (St. Petersburg) and referred to in the literature as the SPD has been preliminarily calibrated by the primary-detector-based method. The possibility of application of SPD photodiodes as radiometric detectors has been investigated. The AXUV-100 photodiode (IRD Inc., United States) was used as a primary detector. The radiation strength of both detectors has been tested. It was revealed that, being more radiation-resistant, the SPD had radiometry characteristics that were not worse than those of the AXUIV-100.     

Multireference State-specific Coupled Cluster Approach with the CAS Reference: Inserting Be into H2

An algorithm for generation of the spin-orbital diagrammatic representation, the corresponding algebraical formulas, and the computer code of the coupled cluster (CC) method with an arbitrary level of the electronic excitations developed earlier in our laboratory have been employed to generate the CAS(2,2)CCSD code. CAS(2,2)CCSD is the state-specific, multireference coupled cluster (SSMRCC) approach with single and double excitations based on the CASSCF(2,2) reference wave function. The CAS(2,2)CCSD was used to describe the model process of inserting the Be atom into the H₂ molecule. We show that our method performs better than the “fully-blown” SSMRCC approach of Mukherjee and coworkers (J Chem Phys 110:6171, 1999).     

Excited states in the multireference state-specific coupled-cluster theory with the complete active space reference

The recently proposed multireference state-specific coupled-cluster theory with the complete active space reference has been used to study electronically excited states with different spatial and spin symmetries. The algorithm for the method has been obtained using the computerized approach for automatic generation of coupled-cluster diagrams with an arbitrary level of the electronic excitation from a formal reference determinant. The formal reference is also used to generate the genuine reference state in the form of a linear combination of determinants contracted to a configuration with the spin and spatial symmetries of the target state. The natural-orbital expansions of the one-electron configuration inferaction density matrix allowed us to obtain the most compact orbital space for the expansion of the reference function. We applied our approach in the calculations of singlet and triplet states of different spatial symmetries of the water molecule. The comparisons of the results with values obtained using other many-particle methods and with the full configuration interaction results demonstrate good ability of the approach to deal with electronic excited states.     

Nonsymmetric Whistler Waves Guided by Cylindrical Ducts with Enhanced Plasma Density

We study the guided propagation of whistler waves whose fields depend on the azimuthal angle in cylindrical plasma-waveguide channels (density ducts) aligned with an external magnetic field and surrounded by a uniform magnetoplasma. The main attention is paid to ducts with enhanced plasma density. It is shown that, under certain conditions, such ducts are capable of guiding proper (eigen) modes and improper leaky modes. We present the results of analysis of the dispersion properties and field structures of nonsymmetric modes guided by cylindrical ducts in the whistler frequency range.     

Automated generation of coupled-cluster diagrams: implementation in the multireference state-specific coupled-cluster approach with the complete-active-space reference

An algorithm for generation of the spin-orbital diagrammatic representation, the corresponding algebraical formulas, and the computer code of the coupled-cluster (CC) method with an arbitrary level of the electronic excitations has been developed. The method was implemented in the general case as well as for specific application in the state-specific multireference coupled-cluster theory (SSMRCC) based on the concept of a "formal reference state." The algorithm was tested in SSMRCC calculations describing dissociation of a single bond and in calculations describing simultaneous dissociation of two single bonds--the problem requiring up to six-particle excitations in the CC operator.