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      • Crystal Structures Created by Builder, CAESAR 1.0
      • The Builder program is used to analyze structural details of a crystalline solid and edit its structure if necessary. Thus the use of Builder may involve the following tasks: (1) to prepare an input file, filename.CI, for a crystal under study, (2) to view the crystal structure and analyze spatial relationships between atoms, and (3) to edit the crystal structure to produce a set of atom coordinates needed for electronic structure calculations.

        Builder lets the user generate an input file, filename.CI, interactively. It allows the user to work with more than one crystal structure at a given time and have multiple views of a given crystal structure. A crystal structure can be viewed in terms of a unit cell or multiple unit cells and can be rotated, translated, and scaled interactively. To facilitate the editing of a current structure on the screen, Builder provides various ways of selecting atoms and bonds from the structure and deleting them. It also enables the user to add atoms to the current structure and replace some atoms of the current structure with other atoms.

        The Builder window has menus File, Build, Display, Setting, and Window (Figure 3.1), and each menu has a set of commands in the drop-down list.

        For more details, please read Chapter 3 of the Manual.

      • Property Plots Created by MP/PP, CAESAR 1.0
      • Solid state materials are often classified according to how their electrical resistivity r varies as a function of temperature T. Metals and semiconductors have positive and negative slopes in their r- versus-T plots, respectively. For some compounds, metallic states are stable only in a certain region of temperature so that a metal may become a semiconductor or a superconductor when the temperature is lowered. In understanding such a phase transition of solid-state materials, it is crucial to know their electronic structures.

        The electronic structure of a molecule is characterized by discrete energy levels and that of a solid by energy bands. Any given energy band consists of N discrete levels, where N is the total number of unit cells in a solid. For all practical purposes, all energy levels falling within a band are allowed because N → ∞. In a one-electron picture of electronic structure, each band level is filled with two electrons. At T = 0 K a normal semiconductor contains only completely filled and completely empty bands, so an energy gap (i.e., band gap Eg) exists between the highest occupied and the lowest unoccupied band levels. A normal insulator has a band gap larger than 2 eV. A normal metal has at least one partially filled band, so there is no energy gap between the highest occupied level (i.e., the Fermi level ef) and the lowest unoccupied level.

        The above discussion is based on one-electron theory, which neglects electron localization resulting from electron-electron repulsion, electron-phonon interaction or random potentials. Magnetic insulators possess unpaired energy levels. Within a one-electron picture, these systems also possess partially filled bands. However, the way the band levels are filled in magnetic insulators is different from that in normal metals. Therefore, when a solid system is predicted to be metallic by one-electron electronic band structure calculations, it is extremely important to recall that such a system may not be a metal but a magnetic insulator. The metallic versus magnetic insulating state of a solid is similar in nature to the low-spin versus high-spin state of a molecule.

        For more details, please read Chapter 4 of the Manual.

      • Fermi Surfaces Created by FP, CAESAR 1.0
      • When a solid possessing a partially filled band is a normal metal (i.e., when the electrons of the partially filled band are not localized), the wave vectors of its FPZ are divided into occupied and unoccupied wave vectors (see Chapter 4). The Fermi wave vectors kF form the boundary between the occupied and unoccupied wave vector regions, and such boundary surfaces are known as Fermi surfaces. All crystal orbital energies calculated for a set of k-points sampling the FPZ are stored in a filename.BE file, which is used to construct the Fermi surfaces of partially filled bands. For 1D chain calculations carried out with a set of k-points in 1D FPZ, the Fermi surface is given by two points kF and -kF. This information is readily obtained when the band dispersion relations are plotted in the vicinity of the Fermi level by running the PP program. The Fermi surface calculation program FC is used only when electronic band structure calculations are carried out for a 2D layer or a 3D solid.

        The FC program generates Fermi surface contours for every partially filled band on certain cross-section planes of the FPZ specified by the user. It requires an input file filename.FI and the filename.BE file produced by the BC program. A Fermi surface of a 3D solid is constructed by combining the Fermi surface contours obtained for a number of cross-section planes slicing the 3D FPZ. These planes are chosen to be parallel to a plane defined by two of the three reciprocal vectors (e.g., a*b*-plane), and their heights along the remaining vector (e.g., c*) are chosen at certain regular intervals (e.g., 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 in units of c*). Note the convention that the a*b*-, b*c*- and a*c*-planes are termed the XY-, YZ- and XZ-planes, respectively.

        The FC program generates two output files, filename.FO and filename.FG. The latter is used by the FP program to display the calculated Fermi surfaces.

        For more details, please read Chapter 8 of the Manual.

      • Density Images Created by DP, CAESAR 1.0

        The PC program performs property calculations (i.e., band dispersion relations, DOS, PDOS, and COOP). It requires an input file filename.PI and the filename.BE, filename.BW and filename.BV files generated by the BC program. The numerical and graphical results produced by the PC program are stored in the files filename.PO and filename.PG, respectively. The file filename.PO can be read by using any text editor, and the filename.PG file is used by the PP program to display plots of band dispersion relations, DOS, PDOS, and COOP.

        For more details, please read Chapter 9 of the Manual.

Crystal Structures Created by Builder, CAESAR 1.0
(BEDT-TTF)2-Cu(NCS)2 (Space-filled) (BEDT-TTF)2-Cu(NCS)2 (Ball/Stick)
C60 Stereoview of Mn2O6 )
Unit cell of [H2N(CH2)4NH2)]V4O9 V4O9(-2) layer

Property Plots Created by MP/PP, CAESAR 1.0
DOS/PDOS of Au2Te12(-4) anion Selected MO/FMOs of (BEDT-TSF)2KHg(SCN)4
DOS of a single graphite layer Dispersion relations of the bands of a 3D graphite layer
PDOS of o-ZrRuP Dispersion relations of t2g bands of WO3 lattice

Fermi Surfaces Created by FP, CAESAR 1.0
LaNiO3 3D Fermi surface k-(BEDT-TTF)2-Cu(NCS)2
WO3(-0.33) LaFe4P12

Density Plots Created by DP, CAESAR 1.0
MoTe2: 3D STM image Relaxed Ti5O10(+14)
Nb3I8 layer Cation of (BEDT-TTF)2-Cu(NCS)2

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