| 1. |
- Karlström, Gunnar, et al.
(författare)
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MOLCAS : a program package for computational chemistry
- 2003
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 28:2, s. 222-239
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Tidskriftsartikel (refereegranskat)abstract
- The program system MOLCAS is a package for calculations of electronic and structural properties of molecular systems in gas, liquid, or solid phase. It contains a number of modern quantum chemical methods for studies of the electronic structure in ground and excited electronic states. A macromolecular environment can be modeled by a combination of quantum chemistry and molecular mechanics. It is further possible to describe a crystalline material using model potentials. Solvent effects can be treated using continuum models or by combining quantum chemical calculations with molecular dynamics or Monte-Carlo simulations. MOLCAS is especially adapted to treat systems with a complex electronic structure, where the simplest quantum chemical models do not work. These features together with the inclusion of relativistic effects makes it possible to treat with good accuracy systems including atoms from the entire periodic system. MOLCAS has effective methods for geometry optimization of equilibria, transition states, conical intersections, etc. This facilitates studies of excited state energy surfaces, spectroscopy, and photochemical processes.
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| 2. |
- Almroth, Per, 1975-, et al.
(författare)
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Modeling of the high temperature behaviour of IN792 in gas turbine hot parts
- 2002
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 25:3, s. 305-315
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The material parameters for two isothermal viscoplastic models with deliberately limited sets of material parameters have been estimated. The models are to describe the behaviour of the nickel based superalloy IN792 in a gas turbine hot part application. The models are based on a power law flow equation and the state variable used is backstress. The model calibration is done by least-squares optimization using non-standard constitutive tests that are aimed at describing relevant component conditions. The constitutive tests give information about the kinematic hardening effects for the backstress evolution equations, while secondary creep data provides stress versus inelastic strain rate information for the flow equation. All tests are uniaxial and isothermal. With the estimated parameter sets the models give relatively good fits to the data. The results suggest that the models can be used to describe the high temperature behaviour of IN792. ⌐ 2002 Elsevier Science B.V. All rights reserved.
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| 3. |
- Berns, H., et al.
(författare)
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A new material for cold forging tools
- 1998
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Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 11:3, s. 166-180
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Tidskriftsartikel (refereegranskat)abstract
- A new tool material for cold forging applications was developed using numerical simulation techniques (FEM) for the design and a powder metallurgical route (HIP) for the production. The basic idea was to find an optimized microstructure of the two phase material by simulating different distributions of hard particles within the metal matrix. On the micro-scale, loading was applied by a field of deformations which was obtained by a macroscopical simulation of a particular cold forming process in bolt making. A new double dispersion microstructure was found to show the best resistance against crack propagation. Specimens were produced by hot isostatic pressing. Afterwards the new material was tested in the laboratory. Wear resistance and bending strength of the double dispersive material are comparable to a standard dispersion material with the same volume fraction of particles, but fracture toughness is increased by about 30%. Testing the new material in bolt making showed that the life time of the tool is increased by a factor of 8.
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| 4. |
- Mackerle, Jaroslav
(författare)
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Finite element analysis and simulation of quenching and other heat treatment processes : A bibliography (1976-2001)
- 2003
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 27:3, s. 313-332
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Forskningsöversikt (refereegranskat)abstract
- This paper gives a bibliographical review of the finite element methods applied to the analysis and simulation of quenching and other heat treatment processes. The bibliography at the end of the paper contains references to papers, conference proceedings and theses/dissertations on the subjects that were published between 1976 and 2001. The following topics are included: quenching - quenching process in general, heat transfer and thermomechanical modelling, residual stresses in quenching, and other topics, hardening, annealing, tempering, and carburizing and nitriding. Three hundred and fifty references are listed. © 2003 Elsevier Science B.V. All rights reserved.
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| 5. |
- Magyari-Kope, B., et al.
(författare)
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Model structure of perovskites : cubic-orthorhombic phase transition
- 2002
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 25:4, s. 615-621
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Tidskriftsartikel (refereegranskat)abstract
- We extend the revised global parametrization method (revGPM) of orthorhombic perovskites with Pbnm symmetry to describe the changes in the lattice parameters and internal atomic coordinates within a broad range of structural distortions, including the vicinity of the orthorhombic-cubic phase transition. The applicability of the revGPM in the prediction of the evolution of the structural parameters under increasing hydrostatic pressure is demonstrated through test calculations performed for geophysically important perovskites. The present results are compared with the available theoretical and experimental data.
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| 6. |
- Nolan, Michael, et al.
(författare)
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Band structure engineering of a molecular wire system composed of dimercaptoacetoamidobenzene, its derivatives, and gold clusters
- 2003
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 27:1-2, s. 166-174
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Tidskriftsartikel (refereegranskat)abstract
- The properties of molecular devices can be engineered through modification of the conformation of the molecule and through chemical substitution. The following study presents the results of density functional theory studies of the properties of a metal-molecule assembly resulting from the interaction between an organic molecular linker, dimercaptoacetoamidobenzene and thirteen atom "magic number" gold nanoclusters. Bonding between two gold nanoclusters, changing the conformation of the linker molecule and the effect of chemical substitution in the linker are assessed through considering the geometry and electronic structure of the resulting assemblies. Changing the conformation in the molecule leads to significant changes in the electronic structure of the metal-linker-metal complex. Chemical substitution in the molecular wire also has an effect on the electronic structure; however, energy level shifts are larger for conformational changes than for chemical substitution
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| 7. |
- Nygårds, Mikael, et al.
(författare)
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Three-dimensional periodic Voronoi grain models and micromechanical FE-simulations of a two-phase steel
- 2002
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 24:4, s. 513-519
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional model is proposed for modeling of microstructures. The model is based on the finite element method with periodic boundary conditions. The Voronoi algorithm is used to generate the geometrical model, which has a periodic grain structure that follows the original boundaries of the Voronoi cells. As an application, the model is used to model a two-phase ferrite/pearlite steel. It is shown that periodic cells with only five grains generate representative stress-strain curves.
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| 8. |
- Vitos, Levente, et al.
(författare)
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Application of the exact muffin-tin orbitals theory : the spherical cell approximation
- 2000
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 18:1, s. 24-38
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Tidskriftsartikel (refereegranskat)abstract
- We present a self-consistent electronic structure calculation method based on the exact muffin-tin orbitals (EMTO) theory developed by O.K. Andersen, O. Jepsen and G. Krier [in: V. Kumar, O.K. Andersen, A. Mookerjee (Eds.), Lectures on Methods of Electronic Structure Calculations, Word Scientific, Singapore, 1994, pp. 63-124] and O.K. Andersen, C. Arcangeli, R.W. Tank, T. Saha-Dasgupta, G. Krier, O. Jepsen and I. Dasgupta [Mater. Res. Sec. Symp. Proc. 491 (1998) 3-34]. The EMTO theory can be considered as an improved screened KKR (Korringa-Kohn-Rostoker) method which is able to treat large overlapping potential spheres. Within the present implementation of the EMTO theory the one-electron equations are solved exactly using Green's function formalism, and Poisson's equation is solved within the spherical cell approximation (SCA). To demonstrate the accuracy of the SCA-EMTO method, test calculations have been carried out.
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| 9. |
- Vitos, Levente, et al.
(författare)
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Stability of fcc (110) transition and noble metal surfaces
- 2000
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Ingår i: Computational materials science. - 0927-0256 .- 1879-0801. ; 17:04-feb, s. 156-159
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Tidskriftsartikel (refereegranskat)abstract
- We have used density functional theory in conjunction with the full charge density linear muffin-tin orbitals method and a cluster expansion based on interatomic pair potentials to derive the energetics of vicinal surfaces on transition and noble metals, and we apply the results in a study of the stability of the fee (1 1 0) facet of these metals against the formation of 'rippled' surfaces consisting of vicinal facets with Miller indices (2 lambda + 1, 2 lambda, + 1,1) and (2 lambda + 1, 2 lambda + 1, (1) over bar).
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| 10. |
- Airiskallio, E., et al.
(författare)
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Magnetic origin of the chemical balance in alloyed Fe-Cr stainless steels : First-principles and Ising model study
- 2014
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 92, s. 135-140
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Tidskriftsartikel (refereegranskat)abstract
- Iron-chromium is the base material for most of the stainless steel grades. Recently, new insights into the origins of fundamental physical and chemical characteristics of Fe-Cr based alloys have been achieved. Some of the new results are quite unexpected and call for further investigations. The present study focuses on the magnetic contribution in the atomic driving forces related to the chemical composition in Fe-Cr when alloyed with Al, Ti, V, Mn, Co, Ni, and Mo. Using the ab initio exact muffin-tin orbitals method combined with an Ising-type spin model, we demonstrate that the magnetic moment of the solute atoms with the induced changes in the magnetic moments of the host atoms form the main factor in determining the mixing energy and chemical potentials of low-Cr Fe-Cr based alloys. The results obtained in the present work are related to the designing and tuning of the microstructure and corrosion protection of low-Cr steels.
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