lecture04.pdf

1、The Nuts and Bolts of First-Principles SimulationDurham,6th-13th December 20014:The New CASTEPCASTEP Developers Groupwith support from the ESF k NetworkNew CAmbridgeSerialTotalEnergyPackageAn introductionThe Nuts and Bolts of First-Principles Durham,6th-13thDecember 2001Lecture 4:Nuts and Bolts 2001

2、Lecture 4:Introduction to New CASTEP?3What New CASTEP is not?Its not just CAmbridge?Its not just Serial?Its doesnt just calculate Total Energies?However,it is still a Package!Nuts and Bolts 2001Lecture 4:Introduction to New CASTEP?4So,What is it Then?Introduction to the CASTEP Developers Group?The g

3、oals of the New CASTEP project?A brief history of New CASTEP?The features of the package?How to use the code(command line)?Philosophy and design of the code?The future of New CASTEPNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?5The CASTEP Developers Group?Mike Payne(Cambridge)?Matt Probert

4、(York)?Chris Pickard(Cambridge)?Stewart Clark(Durham)?Phil Hasnip(Cambridge)?Phil Lindan(Kent at Canterbury)?Matt Segall(Cambridge,Camitro UK Ltd.)Nuts and Bolts 2001Lecture 4:Introduction to New CASTEP?6The Goals of New CASTEP?Ease of maintenance?Ease of future development?Portability?EfficiencyThe

5、se goals are sometimes conflicting,therefore a compromise must be foundNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?7A Brief History of New CASTEP?July 99:A meeting of interested parties.Is there a need for a new PW pseudopotential code?July 99-Jan.00:Informal specification group outlines

6、 the spec.of a new code.?Feb.00:Implementation of new code begins.CDG formed.?May 01:Agreement reached with MSI(Now Accelrys)to commercialise New CASTEP.?Dec.01:Code freeze on first version of New CASTEP.Nuts and Bolts 2001Lecture 4:Introduction to New CASTEP?8New CASTEP Features?Parallel,portable c

7、ode?Geometry Optimisation?BFGS?Damped MD?Molecular Dynamics?NVE?NVT?Linear Response for Phonon spectraNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?9CASTEP Features Continued?Transition state search?LST/QST?Electronic properties?Optical Spectra?DOS?Population AnalysisNuts and Bolts 2001Lec

8、ture 4:Introduction to New CASTEP?10CASTEP Technical Features?Ultrasoft/Norm-conserving pseudopotentials?Pseudopotential generation on-the-fly?Double grid technique for charge/potential grid?Multiple electronic minimisers?All-bands CG?RMM/DIISNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?1

9、1Technical Features Cont?Metals treated by?Density mixing?Ensemble DFT?Exchange-Correlation Potentials?LDA?Perdew-Wang 91 GGA?PBE/RPBE GGA?Non-linear core correctionsNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?12How to Use the Code:The Cell File!Example cell file for primitive SiC%block

10、LATTICE_ABC3.074500 3.074500 3.07450060.0 60.0 60.0%endblock LATTICE_ABC%block POSITIONS_FRACSi 0.00000.00000.0000C0.25000.25000.2500%endblock POSITIONS_FRACNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?13More Cell File KeywordsKPOINTS_MP_GRID 4 4 4%block SYMMETRY_OPS%endblock SYMMETRY_OPS

11、%block SPECIES_POTCmy_C_pot.usp%endblock SPECIES_POTNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?14Controlling the Calculation:The Parameter FileTask:GeometryOptimizationXC_functional PW91Basis_precision PreciseElectronic_minimiser CGElec_energy_tol=0.000001 eVNuts and Bolts 2001Lecture 4

12、:Introduction to New CASTEP?15More ParametersGeom_method BFGSGeom_force_tol:0.01 hartree/bohrFix_occupancies=TRUEContinuation=my_last_run.checkEnergy_unit=kcal/molNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?16Example OutputSummary of cell and parameters input-SCFSCF loop Energy Energy ga

13、in Timer -SCFper atom (sec)-SCF-SCFInitial 6.99675047E+002 4.22 -SCF1 -8.56371636E+002 1.94505835E+002 23.70 -SCF2 -8.57260747E+002 1.11138925E-001 42.59 -SCF3 -8.57286394E+002 3.20580434E-003 62.00 -SCF4 -8.57286462E+002 8.55207285E-006 80.91 -SCF5 -8.57286463E+002 3.12287085E-008 98.20 -SCF-to kin

14、etic energy contributioncall wave_add(wvfn_temp,H_wvfn)!Apply the non-local potential to the wavefunctioncall nlpot_apply(wvfn,wvfn_temp)!Add Vnl|psi to get final H|psicall wave_add(wvfn_temp,H_wvfn)Nuts and Bolts 2001Lecture 4:Introduction to New CASTEP?27Coding Style?Clear code?Meaningful variable

15、 and subroutine names?Lots of comments?Good structure?Care with performance issues?Some features of FORTRAN90 sub-optimal?Use BLAS/LAPACK where applicableNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?28Example problem with F90!Finding the trace of a sub-arrayreal,dimension(N,N):A!Pass a su

16、b-array of A of dimension mtr=bad_trace(A(1:m,1:m),m)!Pass the whole array with dimension of sub-arraytr=good_trace(A,m,N)Nuts and Bolts 2001Lecture 4:Introduction to New CASTEP?29Timings for bad_traceNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?30Timings for good_traceNuts and Bolts 2001Lecture 4:Introduction to New CASTEP?31The Future of New CASTEP?NPT Molecular Dynamics?Free-energy integration for reaction barriers?New non-local XC functionals?NMR chemical shifts?EELS?Raman spectro