# Tag Info

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I agree with the other answer but there are many other resources: Open Crystallographic Database which includes a large set of experimental crystal structures. There's a related Theoretical Crystallographic Open Database For zeolites, there's the IZA Database For MOFs, there's the CoRE MOF database Aflow also has a good repository NOMAD has a variety of ...

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There is the Materials Project: https://materialsproject.org/ From the site: Harnessing the power of supercomputing and state of the art electronic structure methods, the Materials Project provides open web-based access to computed information on known and predicted materials as well as powerful analysis tools to inspire and design novel materials. From ...

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Kohn is easily one of my favorite humans of all time, and he was a role model to whom I looked up in great admiration for most of my academic life; in fact before this site was created, I proposed that we name it after him. However I completely disagree with the sentence that you have quoted. Keep in mind that even though the Nobel Lecture was in 1999, Kohn ...

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I think this question somewhat comes down to what "camp" of DFT progression you subscribe to. I should specify upfront that this summary is mainly centered around molecular systems, so some of the recommendations likely vary for materials where the computational workload can often be much greater. One side really emphasizes accuracy with respect to ...

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2DMatPedia An open computational database of two-dimensional materials. A large dataset of 2D materials, with more than 6,000 monolayer structures, obtained from both top-down and bottom-up discovery procedures 2D structures and layered materials Results from screening all known 3D crystal structures finding those that can be computationally exfoliated ...

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Here is a DFT simulation of a virus, in solution! "Combining Linear-Scaling DFT with Subsystem DFT in Born-Oppenheimer and Ehrenfest Molecular Dynamics simulations: from Molecules to a Virus in Solution." But I like the way Frank Neese (lead author of ORCA) described his coupled cluster calculation of a protein: "this is what I call quantum mechanical ...

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Depending on what kind of materials looking for the following crystallographic databases can be relevant, too (unfortunately, for a cost): Inorganic Crystal Structure Database (ICSD) by Karlsruhe University: https://icsd.products.fiz-karlsruhe.de/ ICSD by FIZ/NIST: https://icsd.nist.gov/ Cambridge Crystal Data Centre (CCDC): https://www.ccdc.cam.ac.uk/

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In addition to above recommendations, I also use American Mineralogist Crystal Structure Database. http://rruff.geo.arizona.edu/AMS/amcsd.php The good thing about this place is that you can check the publications related to a specific geometry. I usually use AMCSD and Materialsproject.

21

I know of several papers over the million-atom mark: 2,097,152 atoms "Calculations for millions of atoms with density functional theory: linear scaling shows its potential" 1,012,500 atoms using linear-scaling orbital-free DFT: "Accurate simulations of metals at the mesoscale: Explicit treatment of 1 million atoms with quantum mechanics" "Million Atom KS-...

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Aligning a molecule to a particular frame of reference (e.g., with the z-axis along a particular bond) is part of Avogadro for this reason: In Avogadro 1.x, there's an align tool You click one atom that will be set to the origin You click another atom that will be projected along the x, y, or z-axis You click 'align' and the molecular coordinates will be ...

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There's three scenarios that come to my mind, for when ab initio methods get abandoned: The cost becomes prohibitive (e.g. too many electrons) The insight is lost It is simply not required for what we want to do Prohibitive cost: If solving the Schrödinger equation (for example) is no longer possible, we may very well still wish we could solve the ...

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I'm not entirely sure what you mean by "universal". If you mean a functional that can model a wide variety of materials with reasonable success, probably the closest we have are GGA functionals. They are not necessarily the most accurate, but they are used to regularly model metals and semiconductors. They get decent results, despite their known ...

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Awesome Materials Informatics The community-edited awesome materials informatics list has a section on "machine-readable datasets", many of which contain atomic structures of materials.

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It is hard to claim that any FCI code overcomes the exponential wall, especially for strongly correlated systems. There are many algorithms, e.g. CDFCI, HCI, FCIQMC, ACI, etc., which significantly reduce the computational cost of direct FCI calculations and represent wavefunctions by sparse vectors. However, in my opinion, all of them only reduce the ...

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SciCalQ The company does more than solving the Schroedinger equation. From its site: SciCalQ’s solid background in computational chemistry and quantum physics own extensive experiences in solving practical and academic problems with scientific computing. They do: Density Functional Theory (DFT) Computation Geometric Configuration: Bond length, bond angle, ...

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There's two facets to this question: What methods can be used for excited states in crystals? (the title, and final sentence) What methods can be used for excited states with plane waves? (paragraphs 1 and 3) I will begin by answering the second question, which is in some sense grounded by this assumption: "it is not possible, as far as I know, to do ...

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The main positives: you can do all-electron calculations you don't need to set up pseudopotentials / PAWs you can study core properties you can use hybrid functionals cheaper / run post-HF calculations The negatives: basis set is geometry dependent, so you get superposition error it's harder to get results close to the complete basis set limit Either ...

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EDIT Doing what you want is hard! You will need a full quantum mechanics based simulation. This is unlikely to be something you can build yourself at the current time. Based on your new additions to the question what you need is Car-Parrinello or Born Oppenheimer MD. These essentially automate the idea of do a quantum electronic structure calculation, take ...

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This paper published by Bikash Kanungo, Paul M. Zimmerman & Vikram Gavini provide an interesting solution to getting closer to a "universal functional" Exact exchange-correlation potentials from ground-state electron densities They have mapped very accurate electronic densities from ab initio full configuration interaction methods onto an exact ...

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Check the USPEX method which is mainly a crystal structure prediction code. It uses the evolutionary algorithm to find the global minimum on the potential energy surface of a material, thereby predicting its crystal structure in the equilibrium state. It works with even a bare-minimum input like the composition of the material. This dissertation (Esfahani, M....

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I agree with Camps that your best bet is to look at a potential advisor and see what they study. Your given example might be a bit of a stretch for some computational materials science advisors, due to its very fundamental nature of solving the problem rather than applying the problem. This could be exactly what one advisor works on though so you should ...

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First, make sure that the structure is correct. Second, make sure that the structure is relaxed. Third, make sure that all the parameters in your input card are reasonable and the used pseudopotentials are matched with your structure. Fourth, make sure that the self-consistent loop is complete, namely, the convergence threshold of the electronic step is ...

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As you mentioned in the question, excitons are indeed bound electron-hole pairs. They are often considered to be the signature of optical spectra in insulating solids. Adding onto the comment by tmph, there are two types of excitons: opposite spins of electrons will lead to a dark exciton with S=0 (since it doesn't allow for momentum conservation). Same spin ...

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Protheragen Protheragen offers a Quantum Chemistry Service which includes: ECD calculation service (absolute configuration determination) Quantitative calculations (quantum chemical calculations) QM, QM/MM, QM/MD Catalytic reaction mechanism calculation Transition state search and energy calculation Chemical reaction pathway and potential energy surface ...

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How to proceed depends on how accurate you want the outcome. Throughout my answer I will provide blue buttons which demonstrate that there's entire tags in our community to address certain aspects of the simulation. What you are describing is (essentially) what we call molecular-dynamics even though you're dealing with atoms rather than molecules. In MD (...

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The only proper way to do it ab initio is to calculate the energy (E) for various internuclear distances (R) and then to approximate the equilibrium bond length by choosing the distance which has the lowest energy, or by fitting the E(R) points to something like a Morse potential (which is decent for short-distances), Lennard-Jones potential (which is decent ...

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Pure plane-wave basis sets have the following advantages when used in periodic DFT (or HF) simulations: Orthogonal Computationally simple (operators with derivatives are particularly straightforward) Low-scaling methods allow easy transformations between real- and reciprocal-space Basis set size does not scale with electron count Independent of atomic ...

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CPMD: Car-Parrinello Molecular Dynamics An approximation of BOMD (Born-Oppenheimer MD) where fictitious dynamics is used on the electrons to keep them close to their ground state, so that we do not have to keep solving for their ground state at every single step. We start with Newton's 2nd law (as does classical MD), but instead of the force being calculated ...

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GHF: Generalized Hartree Fock In Restricted Hartree-Fock (RHF), the molecular orbitals are constructed as pairs, with a single spacial function being used to describe both an $\alpha$ and $\beta$ spin electron. Unrestricted Hartree-Fock (UHF) lifts this requirement, forming a unique set of MOs for $\alpha$ and $\beta$ spin. Generalized Hartree-Fock takes ...

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We attempted to solve a similar problem when studying the (also highly symmetrical) $\ce{CH4}$ and $\ce{CF4}$ homo- and hetero-dimers. I found it easiest to use internal coordinates and fixed molecular geometries to generate the hypersurface, but we also had large computational resources at our disposal and we might have benefitted from using even more, ...

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