I am doing NLO calculations using HF method but i want to do it in DFT method using higher basis set. guide me to this calculations
General Atomic and Molecular Electronic Structure System • General purpose electronic structure code • Primary focus is on ab initio quantum chemistry calculations • Also can do – Density functional theory calculations – Other semi-empirical calculations (AM1, PM3) – QM/MM calculations – Solvent effects REACTION PATHS • Reaction path is least energy path – From reactants (R) through TS to products (P) • Minimum energy path (MEP) • Also called intrinsic reaction coordinate (IRC) • Follows steepest descent path from TS to R or P • Steepest descent means -gradient – IRC = MEP: • Confirms connection between R, TS, P • Provides first step in study of reaction dynamics CORRELATION METHODS • Perturbation theory – E = E(0) + E(1) + E(2) + … • Simplest E(0) = EHF: Then, E(1) = 0 • If series is terminated at second order: MP2 • Series does not always converge well – Best to just stop at MP2 (MP3, MP4 often terrible) • MP2 scales as N5 – Often good compromise between efficiency & accuracy • Includes dispersion naturally • Often over-binds weak interactions (benzene dimer) CORRELATION METHODS • Coupled cluster theory ψ = eTψ0 • ψ0 usually is ψHF • T = cluster operator = T1+T2+T3+…+TN • T1 = sum of 1-particle operators = ∑ti (N4 scaling) • T2 = sum of 2-particle operators = ∑ ∑[tij+ti tj ] (N6 scaling) • T3 = sum of 3-particle operators = ∑ ∑ ∑[tijk+ti tjk+…] (N8) • Approximations • T≈T1 + T2: CCSD (singles (S) + doubles (D)): ~N6 • T ≈T1 + T2 + T3: CCSDT (very expensive): ~N8 • Common compromise: CCSD(T): N7 scaling – Get triples (T) using perturbation theory (not iterative) OVERVIEW OF GAMESS • Types of wavefunctions – Hartree-Fock (RHF, ROHF, UHF, GVB) – CASSCF – CI, MRCI – Coupled cluster methods – Second order perturbation theory • MP2 (closed shells) • ROMP2 (spin-correct open shells) • UMP2 (unrestricted open shells • MCQDPT(CASSCF - MRMP2) – Localized orbitals (SCF, MCSCF) OVERVIEW OF GAMESS • Types of wavefunctions – Fragment Molecular Orbital Theory (FMO) • Enables calculations on very large systems – Thousands of atoms • HF, DFT, MP2 (closed shells) • ROMP2 (spin-correct open shells) • Coupled Cluster methods • MCSCF OVERVIEW OF GAMESS • Energy-related properties – Total energy as function of nuclear coordinates (PES): All wavefunction types – Analytic energy gradient • RHF, ROHF, UHF, MCSCF, CI, DFT • MP2, UMP2, ROMP2 – Analytic Hessian – RHF, ROHF, TCSCF/GVB – MCSCF – Semi-numerical Hessian • MP2, UMP2, ROMP2 - Fully Numerical Hessian - CCSD(T), MRMP2 OVERVIEW OF GAMESS • Energy-related properties (cont’d) – Numerical Hessians from finite differences of analytic gradients – Fully numerical derivatives for all methods – Saddle point (TS) search (requires Hessian) – Minimum energy path=Intrinsic reaction coordinate • Several IRC options - GS2 (default) is most effective • Requires frequency input, gradients along path • Follow reaction path from reactants through TS to products • Build reaction path Hamiltonian (RPH): dynamics OVERVIEW OF GAMESS • Energy-related properties (cont’d) – Dynamic reaction coordinate (DRC) • Add kinetic energy to system at any geometry • Add photon(s) to any vibrational mode • Classical trajectory using QM-derived energies • Requires gradients – Monte Carlo sampling: find global minimum – Molecular dynamics • MM, FMO OVERVIEW OF GAMESS • Other functionalities – Spin-orbit coupling • Any spin states, any number of states • Full two-electron Breit-Pauli • Partial two-electron (P2e)-very efficient, accurate • Semi-empirical one-electron Zeff • RESC • Averaging over vibrational states – Other relativistic effects: Douglas-Kroll to 3rd order – Derivative (vibronic) coupling • MCSCF, MRMP2 OVERVIEW OF GAMESS • Interpretive tools – Localized molecular orbitals (LMO) – Localized charge distributions (LCD) – MCSCF localized orbitals • Nuclear and spectroscopic properties – Spin densities at nucleus (ESR) – NMR chemical shifts – Polarizabilities, hyperpolarizabilities – IR and Raman intensities – Transition probabilities, Franck-Condon overlaps OVERVIEW OF GAMESS • QM/MM Methods – Effective fragment potential (EFP) method for • Cluster studies of liquids • Cluster studies of solvent effects • Interfaced with continuum methods for study of liquids and solvation in bulk • Covalent link for study of enzymes, proteins, materials • General model for intermolecular interactions – SIMOMM: QM/MM method for surface chemistry • QM part can be any method in GAMESS • MM part from Tinker (Jay Ponder - Washington U) • Moving to ReaxFF (Goddard) USING GAMESS • GAMESS runs on – Any UNIX-based system – Any Linux-based system – Any Macintosh – Windows • GAMESS can be downloaded from – www.msg.chem.iastate.edu – License required - no cost USING GAME
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