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DFT COMPUTATIONAL CHEMISTRY

 


The most common question I get from students starting computational chemistry: what do I actually run first?

Here is the answer. Six projects, three phases, two free codes. No expensive licences. No HPC needed for the first four projects.

Phase 1: foundations on your laptop

Project 1: Build and visualise molecules with ASE and VESTA
Start by building H₂O, CO₂, and NH₃ from scratch in Python using the Atomic Simulation Environment. Visualise them in VESTA and Avogadro. Compute bond lengths and angles. Save as XYZ and CIF. This is not optional groundwork. Understanding how atomic coordinates, file formats, and the difference between periodic and molecular systems work will save you from confusion.

Project 2: Your first DFT single point with ORCA
ORCA is free for academic users, developed by Frank Neese's group at the Max-Planck-Institut für Kohlenforschung, and runs entirely on a laptop. Write a five-line input file for H₂O using ! PBE def2-SVP. Run it. Open the output and find the total energy, the orbital energies, and the dipole moment. Understand what the SCF cycle actually produced.

Phase 2: molecular DFT with ORCA

Project 3: Geometry optimisation and IR spectrum
Optimise the CO₂ geometry using ! B3LYP def2-TZVP Opt Freq in ORCA. Compare your computed bond length to the experimental value of 1.16 Ångstrom. Visualise the IR spectrum in Avogadro. If you get an imaginary frequency, understand what it means: your geometry is not a true minimum and you need to displace along that mode and reoptimise.

Project 4: UV-Vis spectrum with TD-DFT
Run a TD-DFT calculation on butadiene or another simple conjugated molecule using ! CAM-B3LYP def2-TZVP TDDFT in ORCA. Plot the absorption spectrum. Identify the dominant excitation and the orbitals involved. This is your first encounter with excited states and why range-separated functionals like CAM-B3LYP matter for charge-transfer-sensitive systems.

Phase 3: periodic DFT with Quantum ESPRESSO

Project 5: K-point and cutoff convergence for silicon
This is the most important practical skill in periodic DFT and almost nobody teaches it explicitly. Run a series of pw.x calculations on bulk silicon varying the k-point mesh from 2×2×2 to 10×10×10 and ecutwfc from 20 to 80 Ry. Plot total energy against each. Identify where the energy stops changing. These are your converged settings.

Project 6: Full workflow: relax, band structure, DOS
Pick any material from the Materials Project. Run vc-relax to relax the structure. Then scf, nscf, bands, dos.x, projwfc.x in sequence. Plot the band structure along the high-symmetry k-path from seekpath. Plot the PDOS. Write a one-page summary comparing your results to the Materials Project reference. This is your first complete periodic DFT workflow from input to interpretation.

Phases 1 and 2 run entirely on a laptop. Phase 3 benefits from HPC access but can be done on a university cluster.

Location: 49 50, Plot No. 44, Mohitewadi Rd, Mohitewadi, Maharashtra 412106, India

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