Elstner_Introduction_DFTB_Part2 - Introduction into DFTB...

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Unformatted text preview: Introduction into DFTB Marcus Elstner July 25, 2006 1 installing dftb dftb is partially written in ratfor, that means it has to be precompiled with ratfor. The ratfor source code is located in DFTB/ratfor compile this an make it available for the makefile of dftb. i.e. move the executable to your bin directory source code is in: DFTB/src/ to compile the code, you have to specify the size: gmake ATOMS=300 ORBITALS=1200 1.1 input for dftb dftb < input > output structure file in gen format is specified in inputfile input The input file contains information about the calculation, i.e. wether a ge- ometry optimization, MD, or single energy evaluation is desired. It further specifies the Slater-Koster parameters to be read, therefore, it determines which atom types are contained in the system. here is an example of an input file: mode max-force scc-on scctol read-charges dispersion external-field-:charges structure.gen charge constraints output.gen L1 L2 L3 L4 ... LN potential:atom 1-atom 1 potential:atom 1-atom 2 1 potential:atom 1-atom 3 ... potential:atom 1-atom N potential:atom 2-atom 1 ... potential:atom 2-atom N potential:atom N-atom 1 ... potential:atom N-atom N stepsize atomic-temperature electronic-temperature scalfactor number-of-steps integer mode: specifies the type of calculation 1 ... MD with scaling of velocities according to atomic-temperature (last line) propability of scaling in each step is given by scalfactor (last line) 2 ... MD without scaling of velocities according to atomic-temperature 3 ... Steepest descent relaxation (velocities are set to zero after each step) 4 ... Conjugate gradient relaxation 5 ... 6 ... Mulliken analysis and atomic energy calculation 7 ... Option number 6 + prints out the eigenvectors 8 ... BFGS relaxation in internal coordinates 9 ... Option number 8 + Z-matrix input 10... Excitation spectrum via linear response 11... Option 1, read and read velocities from VELOC.DAT (restart option) 12... Option 2, read and read velocities from VELOC.DAT (restart option) max-force: If the total force acting on each atom in the structure is smaller than fmax, the conjugate gradient or steepest descent routine is converged and the program terminates. logical scc-on: if .T. self-consistent charge mode: see Elstner PRB 1998 if .F. non-self-consistent charge mode: see Elstner PRB 1995 real scftol: the convergence criterion (Energy) for the charge SCF con- vergence. 2 logical read-charges: dftb outputs a file CHR.DAT, which contains the atomic (Mulliken) charges: if read-charges=.T. this file is read to ac- celerate the initial SCF cycle logical dispersion: enables the use of empirical dispersion energy on top of the DFTB energy function (Elstner et al JCP 2000): needs additional file, see below string external-field-charges: external-field-charges = CH read set of external charges from file EXTCHARGES.INP: next x-1 y-1 z-1 charge-1...
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Elstner_Introduction_DFTB_Part2 - Introduction into DFTB...

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