Experimental data Least bound electrons define Ionization Potential (IP)

Electronic structure depends on:

chemical composition

geometry

Known parameters for diamondoids

-> Calculate IP! Functionals and basis sets How to choose the right functional DFT Output Gaussian Choose the right functional for your problem (e.g. B3LYP)

->exchange-correlation potential

Choose a basis set

->eigenfunction

"draw" your molecule

start calculation and wait... Optimized geometries

Eigenfunctions (i.e. orbitals)

Eigenenergies (e.g. binding energies)

Ionization potentials

Vibrational modes

polarizabilities

and much more... DFT Calculations with Gaussian How to calculate Ionization potentials Schrödinger equation with effective potential Kohn-Sham: electron densities have to match!

-> condition: classical Coulomb repulsion potential of atomic cores exchange-correlation potential self consistent equation: Growing the basis sets functionals represent different ways of exchange-correlation

Approximations for V_XC:

Local density approximation (LDA)

Generalized gradient approximation (GGA)

Mixing of different approximations (hybrid functionals) different parameters (depending on applications)

->different functionals (e.g. B3LYP, M06-2X) Gaussian type orbitals (GTOs) as approximations for Slater type orbitals (STOs)

GTOs are easier to calculate with

problem: GTOs do not "peak"

Use GTOs as basis sets to imitate eigenfunctions

start with small basis sets (e.g. STO-3G)

large basis sets take much cpu time (e.g. 631-G(d,p))

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# DFT calculations with Gaussian09

Short description of basic concepts doing DFT calculations with G09