CASINO manual - Theory of Condensed Matter

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--no-cluster | -l Run the calculation directly on the login node of a cluster without producing a submission script. This option is applied before any others, and makes this script behave as if the machine was a multi-core workstation. --nnode= | -n Set the number of physical, (possibly) multi-core nodes to use to . This will have to be consistent with , , and the machine information in the relevant .arch file. --walltime= | -T Set the wall-time limit for the run to , given in the format [d][h][m][s]. --coretime= | -C Set the core-time (i.e., wall-time times number of reserved cores) limit for the run to , given in the format [d][h][m][s]. --name= | -N Set the submission script name and job name to . Options available on some individual machines If you type runqmc --help you may see appended to the above list a set of additional user-definable options—these all take the form of ‘--user.option’ (and obviously a CASINO ARCH must be defined in order to see these). Such options are defined in the relevant .arch file using the syntax of Appendix 5. The arch system was designed to be readily extensible on a per-machine basis without having to modify any part of the script system that handles it, and thus only variables associated with core functionality are pre-defined, e.g., even the (widely applicable but Linux-specific) nice value of a job on a workstation is handled as --user.nice. Examples of such options include but are not limited to: --user.account Name of account under which to run the job (note that it’s very useful to alias runqmc=’runqmc --user.account=my_account ’ on machines which require it). --user.nice Unix ’nice’ value to use for the job on workstations. --user.queue Name of queue on which to run the job. --user.mem (Over-)estimate of the memory usage per compute node in Mb. --user.shmemsize When running in shared memory mode [on a Blue Gene machine] you are required to set the size of the shared memory partition when launching a job (through the value of an environment variable named BG_SHAREDMEMPOOLSIZE (Blue Gene/P) or BG_SHAREDMEMSIZE (Blue Gene/Q)). The value of this number (in Mb) may be set on the command line as the value of user.shmemsize. See the CASINO FAQ for further details. --user.messagesize Size of MPI message in bytes below which the ’eager’ (truly non-blocking) protocol is used instead of the ’rendezvous’ (partially non-blocking) protocol. Perfect parallel scaling at very large numbers of MPI processes (> c.20,000) with CASINO supposedly requires the non-blocking message passing to be truly asynchronous (i.e., communication takes place at the same time as communication). The default value for MESSAGESIZE on [a Blue Gene/P machine] (1200 bytes) is generally too small, as CASINO config messages typically range up to around 50000 bytes. Thus some advantage may be gained on large numbers of cores by setting MESSAGESIZE to be larger than the default. 28
6.7 How to run coupled DFT-DMC molecular dynamics calculations: the runqmcmd script Coupled DFT-DMC molecular dynamics—which involves a correlated sampling procedure that couples the stochastic imaginary-time electronic and real-time nuclear trajectories—is popularly supposed to result in highly accurate energies for a full dynamical trajectory at a fraction of the cost of doing a full QMC calculation for each nuclear configuration. The basic ideas are outlined in Grossman and Mitas’s paper—Ref. [9]. In my (MDT’s) opinion, this technique is often misrepresented, both by the authors of the GM paper, and by others. It is claimed, for example, in the original paper that: ‘This continuous evolution of the QMC electrons results in highly accurate total energies for the full dynamical trajectory at a fraction of the cost of conventional, discrete sampling.’ ‘[It provides]an improved, significantly more accurate total energy for the full dynamical trajectory.’ ‘This approach provides the same energies as conventional, discrete QMC sampling and gives error bars comparable to separate, much longer QMC calculations.’ A casual reading of the above sentences might lead to the conclusion that we get effectively the same results as conventional DMC at each point along the trajectory. As we are only doing, e.g., 3 DMC stats accumulation per step, we thus appear to be getting ‘something for nothing’. What are we missing? (1) The point about GM-MD—and Lubos Mitas has agreed with this in an email to me—is that its true purpose is to calculate thermodynamic averages, an example being given in the paper of the heat of vaporization of H 2 O. This is calculated as an average over the evolution path of the ions (at a given T > 0) and QMC and thermodynamic averages are done at the same time. Think of it as a method of Monte Carlo sampling a distribution in 3N-dimensional configuration space that is changing shape in time. Each nuclear configuration is sampled via far fewer (e.g., three moves times the number of walkers) electron configurations than usual. It is not intended that accurate energies for all nuclear configurations are calculated, only an accurate Monte-Carlo-sampled ‘thermodynamic average’ as the molecule (or whatever) vibrates or otherwise moves. (2) If you want accurate answers and small error bars for the energies at each point along the MD trajectory then—done under normal conditions (number of DMC walkers etc.)—the method actually does not save you any time at all, apart from that spent doing DMC equilibration. It gives extremely poor answers with huge error bars for the individual MD points; if you want proper DMC accuracy then you have to do the usual amount of statistical accumulation work. (3) The only reason they are able to claim ‘the same energies [and error bars] as conventional, discrete QMC sampling’ is because they use extremely large populations of walkers (a technique which is difficult to scale to large systems). The requirement for a large number of walkers is not stressed in the paper; it is merely stated that ‘we chose a number of walkers such that the statistical fluctuations in the GM-MD energies are one-tenth the size of the variation in the total energy as a function of the MD time with no emphasis that this is considerably more than usual. There is also a big question over whether the configurations read in at the restart can be properly equilibrated in so few moves in the case when the DMC wave functions involve genuinely new physics. MDT has a discussion document in circulation which covers these issues in more detail. Bearing in mind these reservations, the technique has been implemented in casino as follows. The runqmcmd script is used to automate DMC-MD molecular dynamics calculations using casino and the pwscf DFT code (part of the quantum espresso package, available at www.quantum-espresso. org). pwscf must be version 4.3 or later. runqmcmd [--help --nproc_dft=I --splitqmc[=N] --startqmc=M --dft_only/--qmc_only [] We first generate a full DFT trajectory. We then do a full QMC calculation for the initial nuclear configuration of the trajectory, followed by a series of very quick (a few moves) DMC calculations for each point along the trajectory, where each such calculation is restarted from the config.out of the previous one with slightly different nuclear coordinates. This script works by repeatedly calling the runpwscf and runqmc scripts which know how to run pwscf/casino on any individual machine. Almost all optional arguments to this script are the same as for runpwscf/runqmc and are passed on automatically to these subsidiary run scripts (the 29
Page 1 and 2: CASINO User’s Guide Version 2.13
Page 3 and 4: 8.6 GAUSSIAN94/98/03/09 . . . . . .
Page 5 and 6: 29.2 Fourier transformation of CASI
Page 7 and 8: 1 Introduction casino is a computer
Page 9 and 10: 3.2 Legal stuff casino is given awa
Page 11 and 12: - Grossman-Mitas DMC-DFT molecular
Page 13 and 14: Your defined setup can then be perm
Page 15 and 16: - : perform compilation (default).
Page 17 and 18: 6 Introductory user’s guide: how
Page 19 and 20: ATOM BASIS TYPE The basis used to r
Page 21 and 22: ENVMC v0.60: Script to extract VMC
Page 23 and 24: Std. err. in the mean DMC energy (a
Page 25 and 26: Jastrow factor from each cycle of t
Page 27 and 28: V(x) Ψ init (x) τ{ t Ψ 0 (x) x T
Page 29 and 30: the energy becomes roughly constant
Page 31 and 32: many cores, time limits etc, which
Page 33: Set the verbosity level of the mach
Page 37 and 38: unqmcmd --startqmc=M Start the chai
Page 39 and 40: config.out This is the name under w
Page 41 and 42: ‘slater-type’: use Slater-type
Page 43 and 44: CUSTOM SPAIR DEP (Block) This input
Page 45 and 46: initial configurations come from DM
Page 47 and 48: DTDMC (Real) Time step for DMC run
Page 49 and 50: FORCES INFO (Integer) Controls the
Page 51 and 52: nucleus is assumed to lie at the or
Page 53 and 54: MOVIECELLS (Logical) If F then casi
Page 55 and 56: OPT MAXITER (Integer) Largest permi
Page 57 and 58: of G vectors and discards all those
Page 59 and 60: half a million cores, it may be des
Page 61 and 62: VM REWEIGHT (Logical) If vm reweigh
Page 63 and 64: default this is 0 hartree. It shoul
Page 65 and 66: A very detailed specification of th
Page 67 and 68: -1 0 0 1 1 1 1 1 1 1 0 2 1 0 1 2 Pa
Page 69 and 70: cusp conditions; otherwise, only th
Page 71 and 72: Detailed information about each of
Page 73 and 74: |k| (outermost). Hence one can spec
Page 75 and 76: large and the wave function is near
Page 77 and 78: R(i) in atomic units 0.000000000000
Page 79 and 80: 2. The charge-density Fourier coeff
Page 81 and 82: c_767: [ 996 ] ... Compressed expan
Page 83 and 84: valence charges for each atom %%%%%
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1988). This can be found online. An
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1.3813695578425E+00 1.3957621401173
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PWSCF Method: DFT DFT Functional: u
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0.125203784849961E-01 0.13042462855
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3.3000000000000E+00 2.0000000000000
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Potential Number of grid points 200
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9. Clearly, the total number of pos
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EBEST (DMC only) Best estimate of t
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Use G-vector set 1 Number of sets 2
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1000.0 rho_a(G)*rho_b(-G) 16.0 4.12
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total weight must always be include
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The exporter does not currently wor
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8.4.2 Generating gwfn.data files wi
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After successfully running properti
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% mv Test.FChk dna.Fchk run gaussia
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• By default, gaussian uses spin
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Routine Purpose qmc write Writes th
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not the case the defaults can be ch
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8.10 TURBOMOLE Website: www.turbomo
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• crysgen06/09, crystaltoqmc: The
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• quickblock: Simple reblocking u
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• In Movie Settings choose Trajec
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the move rejection probability is h
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This leads to the single-electron d
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In the UNR [19] scheme the modified
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13.7 Evaluating expectation values
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Population-control catastrophes sho
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where u k has the periodicity of th
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Although the constraint equations a
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18 Wave-function updating Consider
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19.2 Evaluating the nonlocal pseudo
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of a unit point charge at r j in ev
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19.4.3 1D Coulomb interaction Coulo
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To investigate whether the extrapol
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correlations, such as might be enco
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where n is the order of the expansi
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terms by definition, and it can be
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which is therefore independent of r
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where the local energy, E L , is E
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Another variant of variance minimiz
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The energy minimization method used
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valid. The first problem, which ari
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• Is emin min energy too high? Th
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It may be activated by setting vmc
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that the number of configuration mo
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• It is possible to use blip orbi
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0.5 0.5 0.0 particle 1 det 1 : 9 or
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The clearup twistav script can be u
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In the infinite system limit, the s
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Note that this has the k −2 diver
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• The effective time step, Eq. (3
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1 2 H He 1.00794 4.00260 3 4 5 6 7
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and the Dirac delta function is δ(
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33.2.2 Atomic densities K eywords:
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The spin-density matrix is a two-by
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33.3.3 Homogeneous and isotropic sy
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33.4 Structure factor and spherical
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33.5 One-body density matrix, two-b
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[ where the approximation ρ (1)T
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The figure shows the localization l
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with F HFT mix = − F P mix = −
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The input keyword to activate the c
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To each walker r j , we assign a li
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37 Magnetic fields and the fixed-ph
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38 Analysis of the performance of C
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the orbitals, α = 2 [11]. The use
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39.2 Implementation basics and perf
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• Use ‘endif’ and ‘enddo’
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• Evidence of testing on serial a
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B Appendix 2: Automatic testing of
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• Delete any eepot.data and densi
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* "Generic" CASINO_ARCHs are intend
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- ‘head -n 1 /etc/redhat-release
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for a single job in an ensemble of
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inary executable. CASINO does not r
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otherwise. The following tags are o
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[2] V.R. Saunders, R. Dovesi, C. Ro
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[50] W. Janke, Statistical Analysis
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CASINO manual - Theory of Condensed Matter

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