1 / 20

Multiply Charged Ions

Multiply Charged Ions. Quantum Chemical Computations Trento, May 2002 Lecture 2. Basis Sets - 1. Usually atom-centered. Basis Sets - 2. l=m=n=o ‘s’ l or m or n = 1 ‘p’ l + m + n = 2 ‘d’ l + m + n = 3 ‘f’. Types of Basis Set. Minimal (one s, p (& d, f) function per shell. STO-3G

selina
Download Presentation

Multiply Charged Ions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Multiply Charged Ions Quantum Chemical Computations Trento, May 2002 Lecture 2

  2. Basis Sets - 1 Usually atom-centered

  3. Basis Sets - 2 l=m=n=o ‘s’ l or m or n = 1 ‘p’ l + m + n = 2 ‘d’ l + m + n = 3 ‘f’

  4. Types of Basis Set • Minimal (one s, p (& d, f) function per shell. STO-3G • Double- (two functions per shell or valence shell). E.g. 3-21G, 6-31G, DZ, SV, … • Triple-, Quadruple- • Polarisation functions: Double- + polarisation (e.g. 6-31G*, 6-31G**, cc-pVDZ, SVP) usually adequate for HF, geometry.

  5. Dynamic Correlation

  6. Correlation

  7. Configuration Interaction

  8. CI • Only CISD practical (partly physically motivated!!) • Slow convergence with basis set size (roughly 1/n3) • Size inconsistent

  9. MPn • Approximate solution to correct Schrödinger equation • Exact solution to a different equation where Vee is replaced by <Vee> • Apply perturbation theory (Møller-Plesset) • To second order (MP2), gives most of the correlation energy in favourable cases

  10. MP2 • Poor performance of MP2 when small band gap • Size consistent

  11. Coupled Clusters

  12. CC Restrict to T2 (CCSD):

  13. CCSD(T) et al. • Only CCSD, CCSD(T) generally feasible • Size consistent • CCSD(T) very accurate where band gap is large (“method of choice”)

  14. Basis Sets and Correlation Slow convergence with basis size!

  15. Correlation Consistent B.S.s T. H. Dunning et al.: • cc-pVDZ: 3s, 2p, 1d (lmax = 2) • cc-pVTZ: 4s, 3p, 2d, 1f (lmax = 3) • cc-pVQZ: 5s, 4p, 3d, 2f, 1g (lmax = 4) • cc-pV5Z: 6s, 5p, 4d, 3f, 2g, 1h (lmax = 5)

  16. Extrapolation

  17. Basis Set Dependence

  18. Other Extrapolation

  19. G2, G3, etc.

  20. G2 EG2 = EQCISD(T)(6-311G**) + E(MP4, diffuse) + E(MP4, 3df) + …

More Related