DFT - CRYSTAL23

A first‑principles computational instrument for predicting structure, bonding, and electronic properties across crystals, surfaces, defects, and heterointerfaces. Our principal engine is CRYSTAL23, a periodic Gaussian‑basis code optimized for hybrid functionals and precise solid‑state simulations.

● Core Function: Compute groundstate energies and relaxed geometries; band structures and densities of states; charge and spin densities; defect formation energies and chargetransition levels; and band offsets/dipoles at interfaces linking atomic structure to measurable optical, electrical, and transport behavior.

● Fundamental Principle: DFT replaces the many electron wavefunction with the electron density and solves the Kohn-Sham equations self consistently using exchange correlation functionals. We routinely employ hybrid DFT (e.g., B3LYP, HSE06 in CRYSTAL23) for accurate band gap and level alignment, with spin polarization when magnetism matters.

● Why it's important: It turns quantum mechanics into design: DFT explains why a measured property emerges and predicts how to tune it accelerating discovery, de risking fabrication, and guiding device architecture without trial and error.

Key Capabilities

Methodology:

Our methodology is rigorous and reproducible centered on DFT. We treat the method like a finely tuned microscope, increasing numerical resolution until the picture stops changing. We test k-point sampling and integration thresholds until energies, forces, and band edges are stable. Structures are relaxed with magnetism explicitly considered when relevant, and electronic smearing is used only when physics demands it for systems with partially filled states. Otherwise, we keep fixed occupations to avoid artificial broadening. Self-consistent iterations use carefully chosen mixing and damping so results converge reliably rather than just quickly. For surfaces and interfaces, we verify vacuum thickness and supercell size. For defects we check interactions between periodic images and align electrostatic potentials to ensure meaningful energetics.

Technologies:

CRYSTAL23 (Core engine)

Method coverage: LDA/GGA/meta-GGA, hybrid DFT (e.g., B3LYP, HSE-06), DFT+dispersion, spin-polarized ground states; non-collinear/spin-orbit where required by the system.
Basis & numerics: All-electron/relativistic Gaussian-type orbitals with well-tested contraction schemes; tight integral thresholds; Monkhorst-Pack k-meshes with systematic convergence, robust SCF controls (smearing, level shifting, damping/mixing).
Properties: Total energies, forces/stress; elastic constants (finite strains), band structures & DOS, charge/spin densities; Mulliken/Löwdin/population analyses, defect formation energies vs. chemical potentials and Fermi level, band alignment and interface dipoles.
Response & spectroscopy (CPHF/CPKS): Frequency-dependent dielectric tensor ε(ω), refractive indices, IR/Raman intensities, polarizabilities, Born effective charges (for lattice contributions), with consistent k-point and basis convergence.
Vibrations & thermodynamics: Γ-point phonons (with supercell workflows for dispersions), vibrational free energies and thermochemical corrections.
Transport (post-DFT): Band velocities and curvature exported for Boltzmann transport pipelines (Seebeck, σ, κ_e in constant-τ), supports screening across temperatures and carrier concentrations.

PYTHON TECHNOLOGIES (workflow + post-processing)

Workflow & reproducibility: Python-driven runners for CRYSTAL23 inputs/outputs, templating of convergence studies, provenance logs, and automated figure generation.
Data toolchain: NumPy, SciPy, pandas for analysis; Matplotlib for publication-grade plots (band structures, DOS, ε(ω), transport maps), custom parsers for CRYSTAL23 outputs.
Quality control: Programmatic convergence sweeps (basis/k-mesh/thresholds), regression tests on reference cells, and CI-friendly notebooks to ensure repeatable results.

CRYSTAL MAKER (modeling & visualization)

Structure building, rapid construction of supercells, slabs, terminations, grain boundaries, and defect models with symmetry tools.
High-quality renderings, animations of relaxations, and slices for charge or spin density; ideal for figures and outreach.
Interoperability, import/export of CIF and common formats, clean handoff to DFT workflows, and snapshot generation for documentation.

Research Applications

Structure & Energetics: Total energies; forces and stress; equation-of-state curves; elastic constants (from finite distortions); cleavage/surface energies.

Electronic Structure: Band structures along high-symmetry paths; densities of states (total & projected); band-edge character and effective masses; charge and spin densities; population analyses.

Defects & Doping: Formation energies vs. chemical potentials and Fermi level; charge-transition levels; supercell image corrections where applicable; local relaxations and level alignment.

Interfaces: Band offsets (potential-lineup and projection-based), interface dipoles and built-in fields; layer-resolved potentials and densities.

Response Properties via CPHF/CPKS (CRYSTAL23):
- - High-frequency dielectric tensor ε∞ and frequency-dependent permittivity ε(ω).
  - Refractive indices and optical spectra (real/imaginary parts).
  - Polarizabilities; IR and Raman intensities (Γ-point).
  - Born effective charges (from finite-field/response workflows) and related lattice contributions to static dielectric response when required.

Vibrations & Thermodynamics: Γ-point phonons (with supercell/phonopy interfaces for dispersions), vibrational thermochemistry from density-functional frequencies.

Transport (Boltzmann formalism): Using band energies and velocities, we compute Seebeck coefficient, electrical conductivity, and electronic thermal conductivity within the constant-relaxation-time approximation (post-processing via our Boltzmann transport workflow).

Spectral & Derived Maps: Real-space isosurfaces/slices for charge/spin densities and difference densities; work-function maps for slabs; potential landscapes across heterostructures.

Reproducibility Artifacts: Input files, k-path definitions, convergence records, and plotting scripts suitable for archiving and open-data release.

Related Publications

Impact of Ni and O vacancies on the electronic properties of NiO: A DFT-based study for optoelectronic applications. F. Bermúdez-Mendoza, D.J. Ramos-Ramos, M. Taeño, G.C. Vásquez, D. Maestre, F Domínguez-Adame, B. Méndez, R. Martínez-Casado, E. Díaz. APL Materials 13, 9 (2025).
Engineered Optical and Electronic Properties in β-Ga₂O₃/SnO₂ Nanowire Networks. J. Dolado, P. Pérez-Peinado, D. Carrasco, R. Martínez-Casado, V. Bonino, J. Segura-Ruiz, B. Méndez. Nano Letters 25, 11299 (2025).
Micro- and nano-Zn₂GeO₄ as new material for optoelectronic applications. P. Hidalgo, J. Dolado, R. Martínez-Casado, B. Méndez. Proc. SPIE Oxide-based Materials and Devices XVI 13367, 112 (2025).
First-principles study of the structural, electronic, and optical properties of Ga₂O₃. F.B. Mendoza, R. Martínez-Casado, E. Nogales, B. Méndez. Proc. SPIE Oxide-based Materials and Devices XVI 13367, 1336702 (2025).
Proving Optical Anisotropy and Polarization Effects in β-Ga₂O₃ Nanomembranes via X-Ray Excited Optical Luminescence. P. Pérez-Peinado, J. Dolado, P.L. Alcázar-Ruano, D. Carrasco, R. Martínez-Casado, E. Nogales, B. Méndez. Advanced Photonics Research 5, 2500043 (2025).
Study of the microstructure and temperature dependent luminescence of Na-and Li-beta gallia rutile compounds. M. Garcia-Carrion, R. Martinez-Casado, E. Nogales, and B. Mendez. Materialia 38, 102302 (2024).
Effect of Li-doping on the optoelectronic properties and stability of tin (II) oxide (SnO) nanostructures. A. Vázquez, R. Martínez-Casado, A. Cremades, and D. Maestre. Journal of Alloys and Compounds 959, 170490 (2023).
Interplay between crystal structure and optical response in Plateau–Rayleigh Zn2GeO4/SnO2 heterostructures. J. Dolado, F. Malato, J. Segura-Ruiz, M. Taeño, I. Snigireva, P. Hidalgo, B. Méndez, and G. Martínez-Criado. Advanced Photonics Research 4, 2300063 (2023).
Li-doping effects on the native defects and luminescence of Zn2GeO4 microstructures: Negative thermal quenching. J. Dolado, B. Rodriguez, R. Martinez-Casado, I. Pís, E. Magnano, P. Hidalgo, and B. Méndez. Acta Materialia 245,118606 (2023).
Optical anisotropy and refractive index dispersion of Zn2GeO4 microrods. J. Dolado, R. Martinez-Casado, P. Hidalgo, and B. Méndez. Optical Materials Express 13, 3156 (2023).
Ethanol gas sensing mechanisms of p-type NiO at room temperature. J. Bartolomé, M. Taeno, R. Martinez-Casado, D. Maestre, and A. Cremades. Applied Surface Science 579, 52134 (2022).
Persistence of symmetry-protected Dirac points at the surface of the topological crystalline insulator SnTe upon impurity doping. O. Arroyo, Y. Baba, J. Cerdá, O. de Abril, R. Martínez-Casado, F. Dominguez-Adame, and L. Chico. Nanoscale 15, 3566 (2022).
Unravelling the role of lithium and nickel doping on the defect structure and phase transition of anatase TiO2 nanoparticles. A. Vázquez, R. Martinez-Casado, D. Maestre, J. Ramirez, I. Pís, S. Nappini, and A. Cremades. Journal of Materials Science 57, 7191 (2022).
Influence of cation substitution on the complex structure and luminescent properties of the ZnkIn2Ok+3 system. J. Garcia, A. Torres, J. Bartolome, R. Martinez-Casado, Q. Zhang, J. Ramirez-Castellanos, O. Terasaki, A. Cremades, and J. M. Gonzalez-Calbet. Chemistry of Materials. 32, 6176 (2020).
Understanding the UV luminescence of zinc germanate: the role of native defects. J. Dolado, R. Martínez Casado, P. Hidalgo, R. Gutiérrez, A. Dianat, G. Cuniberti, F. Domínguez-Adame, E. Díaz, and B. Méndez. Acta Materialia 196, 626 (2020).
New insights into the luminescence properties of a Na stabilized Ga–Ti oxide homologous series. J. García-Fernández, M. García-Carrión, A. Torres-Pardo, R. Martínez-Casado, J. Ramírez-Castellanos, E. Nogales, J. González-Calbet, and B. Méndez. Journal of Materials Chemistry C 8, 2725 (2020).

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