Der Einsatz der Dichtefunktionaltheorie in der Materialphysik: Ein atomistischer Blick auf moderne Werkstoffe Slide 1
Inhalt I. Atomistische Modellierung von Materialien II. Dichtefunktionaltheorie (DFT) III. Anwendungen Slide 2
0.1 nm 1 nm 10 nm 100 nm 1 m 10 m 100 m 1 mm 10 mm 100 mm Length Scales in Materials Modelling Juan J. de Pablo and William A. Curtin, Guest Editors, MRS Bulletin 32 (Nov. 2007) Slide 3
Length Scales in Materials Modelling Continuum Mechanics 0.1 nm 1 nm 10 nm 100 nm 1 m 10 m 100 m 1 mm 10 mm 100 mm Finite Element Methods Juan J. de Pablo and William A. Curtin, Guest Editors, MRS Bulletin 32 (Nov. 2007) Slide 4
Length Scales in Materials Modelling Mesoscale 0.1 nm 1 nm 10 nm 100 nm 1 m 10 m 100 m 1 mm 10 mm 100 mm dislocation models Juan J. de Pablo and William A. Curtin, Guest Editors, MRS Bulletin 32 (Nov. 2007) Slide 5
Length Scales in Materials Modelling Nanoscale 0.1 nm 1 nm 10 nm 100 nm 1 m 10 m 100 m 1 mm 10 mm 100 mm dislocation plasticity and atomistic models coexist Juan J. de Pablo and William A. Curtin, Guest Editors, MRS Bulletin 32 (Nov. 2007) Slide 6
Length Scales in Materials Modelling Quantum Scale 0.1 nm 1 nm 10 nm 100 nm 1 m 10 m 100 m 1 mm 10 mm 100 mm Ab-initio electronic structure methods Juan J. de Pablo and William A. Curtin, Guest Editors, MRS Bulletin 32 (Nov. 2007) Slide 7
From First Principles Coulomb Force = Slide 8
From First Principles Coulomb Force = type of bonding Quantum Mechanics + crystal structure elastic constants lattice vibrations band structure Slide 9
Born Oppenheimer Approximation He atom (schematically) Born Oppenheimer approximation electrons QM de Broglie wavelength nuclei classical (Newton) Slide 10
Born Oppenheimer Approximation He atom (schematically) The Born Oppenheimer (=adiabatic) Approximation The electrons can follow the much heavier nuclei instantaneously Electronic and nuclear motion can be separated Slide 11
A Simple Example: H2 Molecule Total Electronic Hamiltonian H2 molecule e p+ p+ e 2 electron Schrödinger equation Slide 12
Many Electron Problem Total Electronic Hamiltonian e Zp+ Many electron Schrödinger equation Slide 13
Van Vleck Catastrophe Small molecules Wave function methods (HF, configuration interaction,...) give excellent results Number of parameters in many electron wave function: M = p3n Large molecules and solids Many electron wave function is not a legitimate concept when N > 100 Number of parameters in wave function: M = p3*100 = 10150!! Accuracy of the wave function becomes a problem! Storage of the results: B = q3*100 = 10150 bits required!! Slide 14
Electron Density as a Loophole Electron Density in a (10,0) single walled Carbon Nano Tube Electron density n(r) is the basic variable Density Functional Theory (DFT) provides rigorous framework All microscopic and macroscopic properties depend on n(r) Slide 15
Inhalt I. Atomistische Modellierung von Materialien II. Dichtefunktionaltheorie (DFT) III. Anwendungen Slide 16
Hohenberg Kohn Theorem universal functional of the electron density external potential due to atomic nuclei The total energy of a system of interacting electrons is a functional of the density. The energy takes its minimum at the ground state density. Slide 17
Hohenberg Kohn Theorem universal functional of the electron density external potential due to atomic nuclei The total energy of a system of interacting electrons is a functional of the density. The energy takes its minimum at the ground state density. Suggestion of Kohn and Sham: exchange correlation energy Slide 18
Kohn Sham Equations Replace the system of interacting electrons by a fictitious system of non interacting electrons with the same density Single electron Schrődinger equations with an effective potential Slide 19
Kohn Sham Equations Atomic nuclei Slide 20
Kohn Sham Equations Atomic nuclei Hartree potential Slide 21
Kohn Sham Equations Atomic nuclei Hartree potential classical electro static interactions Exchange correlation potential Quantum mechanical effects Slide 22
Kohn Sham Equations Self consistency Slide 23
Kohn Sham Equations Self consistency Approximations Slide 24
Exchange Correlation Functionals First Generation (1980) Local Density Approximation (LDA) Slide 25
Exchange Correlation Functionals First Generation (1980) Second Generation (1996) Local Density Approximation (LDA) Generalized Gradient Approximation (GGA) Slide 26
Exchange Correlation Functionals First Generation (1980) Second Generation (1996) Third Generation (1999) Local Density Approximation (LDA) Generalized Gradient Approximation (GGA) Orbital dependent exchange e.g.: PBE0 = *Hartee Fock exchange + (1 )GGA Slide 27
DFT in a Nutshell Walter Kohn Rev. Mod. Phys. 71, 1253 (1999) atomic nuclei electrons DFT Nobelprize 1998 Walter Kohn Slide 28
Numerical Solution Slide 29
Numerical Solution Expansion in a basis Matrix Eigenvalue Problem Property typically around 100 basis functions per atom Slide 30
High Performance Computing IBM Power 5+ System 74 Computing Nodes 300 Computer Cores about 1000 GByte RAM 9 TByte Storage 1.5 TeraFLOP 600 000 Euro Slide 31
DFT Codes PW PP PAW FP LAPW plane wave pseudo potentials projector augmented wave full potential LAPW PWscf CP PAW WIEN2k http://www.pwscf.org/ http://www2.pt.tu clausthal.de/atp/ http://www.wien2k.at/ ABINIT http://www.abinit.org/ VASP http://cms.mpi.univie.ac.at/vasp/ http://exciting code.org/ Slide 32
Inhalt I. Atomistische Modellierung von Materialien II. Dichtefunktionaltheorie (DFT) III. Anwendungen Slide 33
What can be calculated? Structural Properties Lattice Parameters Elastic Constants Atomic Forces, Equilibrium Geometry Surface Relaxations Defect Structures Lattice Dynamics Vibrational Frequencies Phonon DOS, Vibrational Entropy Electron Density Charge Rearrangements Electric Field Gradients Electronic Structure Band Structure Density of States Spectroscopy Photoemission Electron Energy Loss Optical Absorption Dielectric Function Core Level Spectroscopies Raman Scattering Compton Scattering Positron Annihilation Slide 34
Applications A) Fe Si Alloys: Lattice Constants / Bulk Modulus B) Fe Mn Austenite Steel: Stacking Fault Energy C) Organic Semiconductors: Cohesive and Adsorption Energies Slide 35
Bulk Cu: Total Energy vs. Volume body centred cubic face centred cubic Slide 36
Bulk Modulus of Copper bcc aexp = 3.60 Å adft = 3.63 Å fcc Bexp = 142 GPa BDFT = 139 GPa Slide 37
FeSi Alloys Zhang, Puschnig, Ambrosch Draxl (submitted) Slide 38
Stacking Faults in Austenite Steel A C B A B A C B A Motivation: Development of TWIP steels which combine high strength with high formability Slide 39
Stacking Faults in Austenite Steel 2 cm Picture from: Ausgekochter Stahl fűr das Auto von morgen, G. Frommeyer, MaxPlanckForschung 3/2004 A C B A B A C B A Motivation: Development of TWIP steels which combine high strength with high formability Slide 40
Stacking Faults in Austenite Steel A C B A B A C B A Axial Interaction Model [Denteneer et al., J. Phys. C Sol. St. Phys. 20, L883 (1987)] ~ hcp + 2Fdhcp 3Ffcc SFE = F Temperature Dependence F = E T S Magnetic entropy from DFT + Monte Carlo simulations Total energy from DFT Slide 41
Stacking Faults in Austenite Steel Reyes Huamantinco, Ruban, Puschnig, Ambrosch Draxl, to be published Slide 42
Organic Semiconductors Sample of a 10x10 cm2 white OLED (from HC Starck CleviosTM PH510 PEDOT layer) Samsung ultra thin 0.05mm 4 inch OLED display (480 272 resolution, 100,000:1 contrast, 200cd/m2) Organic Solar Cell (Linz Institute for Solar Cells) The work is part of the National Research Network Interface controlled and functionalized organic films Slide 43
Organic pi Conjugated Molecules Pentacene (C22H14) OFET Organic Field Effect Transistor Para Sexiphenyl (C36H26) 2.6 nm OLED Organic Light Emitting Diode Slide 44
Cohesive Energy of Molecular Crystals Pentacene Crystal Structure Ecrystal Slide 45
Cohesive Energy of Molecular Crystals Pentacene Crystal Structure Ecohesive = [ (1/2) Ecrystal Emolecule ] Slide 46
Cohesive Energy of Molecular Crystals Slide 47
Van der Waals Density Functional Exchange Correlation Energy Nonlocal Correlation Energy leading to van der Waals interaction Dion et al, Phys. Rev. Lett. 92, 246401 (2004). Slide 48
Cohesive Energy of Molecular Crystals Nabok, Puschnig, Ambrosch Draxl, Phys. Rev. B 77, 245316 (2008). Slide 49
Surface Energy of Molecular Crystals d Nabok, Puschnig, Ambrosch Draxl, Phys. Rev. B 77, 245316 (2008). Slide 50
Thiophene / Cu(110) d Slide 51
Thiophene / Cu(110) d Sony, Puschnig, Nabok, Ambrosch Draxl, Phys. Rev. Lett. 99, 176401 (2007). Slide 52
Summary Electronic structure calculations are the first step in a multi scale approach towards computational materials design Density Functional Theory is the standard framework for the calculation of ground state properties from first principles Various materials properties can be obtained from DFT total energy and force calculations Strong predictive power of DFT since it involves no empirical parameters Further developments in Exc are needed to improve accuracy Slide 53
NiTi Shape Memory Alloys Slide 54
Elastic Constants stress strain Hooke's Law stress = F/A ut tensio sic vis (1678) F strain = l/l Slide 55
Elastic Constants stress strain Hooke's Law ut tensio sic vis (1678) Cubic Crystal 3 different components Slide 56
Elastic Constants stress strain Hooke's Law ut tensio sic vis (1678) Monoclinic Crystal 13 different components Slide 57
Elastic Constants Special Strains z y x Total Energy Monoclinic Crystal 13 different components Slide 58
NiTi Shape Memory Alloys Golesorkhtabar, Spitaler, Puschnig, Ambrosch Draxl, to be published Slide 59