5 slides about: Computational Chemistry for Inorganic Chemists

1. 5 slides about: Computational Chemistry for Inorganic Chemists

2. Computational vs. Experimental Methods

3. Choice of Method and Basis Set Which method? • • We’re using Density Functional Theory (DFT) as it gives us the most accurate results for transition metals in the least amount of time. We’re using the B3LYP flavor of DFT as it is the most common one. Which basis set?  Basis sets are approximations of atomic orbitals • • We will be using LANL2DZ for our calculation as it models the bonding in transition metal complexes well. What job type? • Geometry Optimize + Vibrational Frequencies (for reactants or products)

4. We are calculating points on the Potential Energy Surface (PES): Energy and other properties are a function of geometry Local maxima Saddle Point

5. Geometry Optimization Maxima and Minima are stationary points (1st derivative of PES =0) • Minima gives equilibrium structure(s) of reactant or product; must have NO imaginary frequencies • Saddle point corresponds to transition structure; transition states should have ONE imaginary frequency Input Initial Guess Gaussian calculates Integrals Stationary Point reached? You’re Done! YES NO New Geometry Guess

6. Analysis: Geometry Optimized? Should see something like: Item Value Threshold Converged? Maximum Force 0.000005 0.000450 YES RMS Force 0.000002 0.000300 YES Maximum Displacement 0.000012 0.001800 YES RMS Displacement 0.000006 0.001200 YES Predicted change in Energy=-1.586489D-10 Optimization completed. -- Stationary point found. Is it a minima? Search for NImag (Should be 0 for minima) \NImag=0\ Want thermochem data? Search raw output for Kcal Zero-point vibrational energy 53572.7 (Joules/Mol) 12.80419 (Kcal/Mol) … Thermal correction to Gibbs Free Energy= -0.006541 Sum of electronic and zero-point Energies= -997.086339 Sum of electronic and thermal Energies= -997.080515 Sum of electronic and thermal Enthalpies= -997.079571 Sum of electronic and thermal Free Energies= -997.113285 Anything else? Click on the magnifying class to the right of your job in WebMO

7. Typical units in computational programs Bohr: Atomic unit of Length (a0) • Equal to the radius of the first Bohr orbit for a hydrogen atom • 5.29 x 10-11 m (0.0529 nm, 52.9 pm, 0.529 Å) Hartree: Atomic unit of Energy •  Equal to twice the energy of a ground state hydrogen atom • 627.51 kcal/mole • 2625.5 kJ/mole • 27.211 eV • 219474.6 cm-1