CASINO manual - Theory of Condensed Matter

More documents

Recommendations

Info

lattice points of the supercell offset by a constant vector k s in the first Brillouin zone of the simulation cell. In an explicitly correlated method such as QMC the need to describe long-range correlations forces one explicitly to construct a simulation supercell consisting of several primitive cells. By contrast, in single-particle methods such as DFT, the problem can be reduced to a single primitive cell with a grid of k points, and the simulation supercell is never explicitly constructed. You could generate a trial wave function for use in your QMC calculation by performing a DFT calculation for the simulation supercell at a single k point. However this would be inefficient: the translational symmetry within the simulation cell would not be exploited to reduce memory requirements in both the DFT calculation and the subsequent QMC calculation. Instead you should generate the trial wave function for a simulation supercell consisting of l × m × n primitive cells by performing a DFT calculation in a single primitive cell with an l × m × n mesh of k points. In summary, your DFT calculation should be set up to generate a set of orbitals for a single primitive unit cell with an l × m × n k-point grid, whilst the QMC calculation should be set up for a simulation supercell consisting of l × m × n primitive cells. In the input file, the number of up- and down-spin electrons neu and ned should be appropriate for the supercell, whilst the npcell block, which specifies the size of the supercell, should contain ‘l m n’. Note that QMC methods cannot exploit symmetry (apart from time-reversal symmetry), and hence a complete l × m × n grid of k vectors must be supplied in general. (How you do this depends on your DFT code.) If you are using a grid of k vectors with time-reversal symmetry then your trial wave function in the subsequent QMC calculations can be chosen to be real, and the complex wf input keyword should be set to F. In this case you only need to supply one out of each ±k pair. If you do not have time-reversal symmetry you must supply the complete grid of k vectors and set the complex wf keyword to T. Typically you will need to perform QMC calculations in two different supercell sizes and extrapolate your results to the limit of infinite cell size. How exactly you proceed depends a good deal on what you are calculating. The problem of finite-size errors in QMC calculations is discussed extensively in Ref. [14]. 6.6 How to run the code: RUNQMC The runqmc script (which should be in your path after installing casino) is designed to reduce the effort of doing QMC calculations to just entering one command. It is most useful when using parallel machines with a batch queueing system. It is written to detect all common errors that a user may make in setting up a calculation, so that the fault is detected immediately rather than when the batch job starts (which may be many hours later). See the utils/runqmc/README file for more information. runqmc can run calculations on single- and multiprocessor workstations, and on clusters. To run the casino calculation set up in the current directory, simply type runqmc. This will automatically—and possible a little dangerously—occupy all cores on a workstation, or the maximum permitted allocation (in both number of cores and walltime) on a cluster. To change this, or to specify other calculation parameters, there are various options available. An example on a big parallel machine: runqmc --nproc=224256 --walltime=10h --shm=12 will run the code in parallel using 224256 MPI processes (distributed among computational nodes depending on the number of cores per node in the machine, which runqmc knows about) using shared memory over groups of 12 processes with a walltime limit of 10 hours (which may affect what queue your job is put in). Note that this is equivalent to runqmc -p 224256 -T 10h -s (provided the machine has 12 cores per node) i.e., most options come with a longer version (with two hyphens and an equals sign) and a shorter easier-to-type version (with one hyphen, and zero or more spaces before the option value). A really important point which trips quite a few people up: on machines with batch queue systems everyone is used to manually creating batch scripts which tell the machine how to run the code, how 24
many cores, time limits etc, which is then manually qsubbed to the batch queue. Do not insert a call to runqmc in such a script ( c○the casino Wiki on the UK national facility ‘Hector’, written by the sysadmins). The purpose of runqmc is to create this batch script, and runqmc will then submit it all by itself. OK? We appreciate this is unusual, but it works. If you can’t remember the basic parameters of the machines that you’re running on (e.g., the number of cores per node, queue-dependent walltime limits, the maximum number of cores etc.) then typing runqmc --info or runqmc -i will print to the screen all relevant parameters available from the machine’s arch file. This may help you decide on what values to use for the run time parameters when invoking runqmc. 6.6.1 Other facilities (1) runqmc can run calculations in multiple directories, by simply giving the directory names at the end of the command line, e.g., runqmc -p 256 -T 10h diamond beta_tin will run the two calculations in directories ‘diamond’ and ‘beta tin’, where each of them uses 256 cores. Running, e.g., 2 calculations on a 4-core workstation will result in 2 cores being used for each of them (unless otherwise specified via ‘-p’). Running multiple calculations on clusters is only possible for specific machines; multiple calculations on clusters will use a single batch queue slot and a single script. This is useful for large clusters where runs on large numbers of cores are cheaper per core-hour by policy, but is otherwise a bad idea since different calculations will take different times to complete but the longest will be charged for. If no directories are specified, the calculation in the current directory will be run. (2) In order to run on a cluster log-in node, use the ‘--no-cluster’ option, which will make runqmc behave as if the machine was a workstation. You should check with your system administrator to see if this is OK. (3) If you would like to produce a submission script on a cluster without running casino (for verification purposes), use the ‘--check-only’ flag. (4) In order to use the OpenMP capabilities of casino, use the flag ‘--tpp=〈threads-per-process〉’. runqmc will automatically adjust the number of processes per node to leave one OpenMP thread per core. If you would like to modify this behaviour, use the ‘--ppn=〈processes-per-node〉’ flag and set your own value. You need to have compiled the OpenMP version with ‘make Openmp’ in order to access this feature. (5) In order to use the shared-memory capabilities of casino, use the flag ‘--shm’. runqmc will tell casino to share orbital coefficients (blip or Gaussian only) and some other data among all cores in each node; to modify this behaviour use instead ‘--shm=〈number-of-cores-in-SHM-group〉’. You need to have compiled the SHM version with ‘make shm’ in order to access this feature (‘make OpenmpShm’ is also available). (6) Individual machines can have user-defined options --user.option in order to cope with particular idiosyncrasies. See the end of the Usage section below. (7) A similar script ‘runpwscf’ is available for running the pwscf plane-wave DFT-code, which also uses the same CASINO ARCH system for determining what computer we’re running on. It has the same set of optional arguments as runqmc, apart from the obviously QMC-specific ones (plus some extra ones for controlling pwscf behaviour). Note that if your casino arch file defines a command for running casino, then it must include a tag &BINARY ARGS& following the &BINARY& tag; this is because the pwscf executable takes command line arguments such as -pw2casino, -npool etc., which are not required by casino. (8) A script ‘runqmcmd’ is available which runs coupled DFT-DMC molecular dynamics calculations (see section6.7). This exploits both ‘runpwscf’ and ‘runqmc’ to alternately run pwscf DFT calculations and casino QMC calculations. (9) A script ‘twistav pwscf’ is available for running ‘twist-averaged’ calculations where new xwfn.data files are repeatedly generated by pwscf for different twist angles (offsets of the k-point 25
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: the energy becomes roughly constant
Page 33 and 34: Set the verbosity level of the mach
Page 35 and 36: 6.7 How to run coupled DFT-DMC mole
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 %%%%%
Page 85 and 86:
1988). This can be found online. An
Page 87 and 88:
1.3813695578425E+00 1.3957621401173
Page 89 and 90:
PWSCF Method: DFT DFT Functional: u
Page 91 and 92:
0.125203784849961E-01 0.13042462855
Page 93 and 94:
3.3000000000000E+00 2.0000000000000
Page 95 and 96:
Potential Number of grid points 200
Page 97 and 98:
9. Clearly, the total number of pos
Page 99 and 100:
EBEST (DMC only) Best estimate of t
Page 101 and 102:
Use G-vector set 1 Number of sets 2
Page 103 and 104:
1000.0 rho_a(G)*rho_b(-G) 16.0 4.12
Page 105 and 106:
total weight must always be include
Page 107 and 108:
The exporter does not currently wor
Page 109 and 110:
8.4.2 Generating gwfn.data files wi
Page 111 and 112:
After successfully running properti
Page 113 and 114:
% mv Test.FChk dna.Fchk run gaussia
Page 115 and 116:
• By default, gaussian uses spin
Page 117 and 118:
Routine Purpose qmc write Writes th
Page 119 and 120:
not the case the defaults can be ch
Page 121 and 122:
8.10 TURBOMOLE Website: www.turbomo
Page 123 and 124:
• crysgen06/09, crystaltoqmc: The
Page 125 and 126:
• quickblock: Simple reblocking u
Page 127 and 128:
• In Movie Settings choose Trajec
Page 129 and 130:
the move rejection probability is h
Page 131 and 132:
This leads to the single-electron d
Page 133 and 134:
In the UNR [19] scheme the modified
Page 135 and 136:
13.7 Evaluating expectation values
Page 137 and 138:
Population-control catastrophes sho
Page 139 and 140:
where u k has the periodicity of th
Page 141 and 142:
Although the constraint equations a
Page 143 and 144:
18 Wave-function updating Consider
Page 145 and 146:
19.2 Evaluating the nonlocal pseudo
Page 147 and 148:
of a unit point charge at r j in ev
Page 149 and 150:
19.4.3 1D Coulomb interaction Coulo
Page 151 and 152:
To investigate whether the extrapol
Page 153 and 154:
correlations, such as might be enco
Page 155 and 156:
where n is the order of the expansi
Page 157 and 158:
terms by definition, and it can be
Page 159 and 160:
which is therefore independent of r
Page 161 and 162:
where the local energy, E L , is E
Page 163 and 164:
Another variant of variance minimiz
Page 165 and 166:
The energy minimization method used
Page 167 and 168:
valid. The first problem, which ari
Page 169 and 170:
• Is emin min energy too high? Th
Page 171 and 172:
It may be activated by setting vmc
Page 173 and 174:
that the number of configuration mo
Page 175 and 176:
• It is possible to use blip orbi
Page 177 and 178:
0.5 0.5 0.0 particle 1 det 1 : 9 or
Page 179 and 180:
The clearup twistav script can be u
Page 181 and 182:
In the infinite system limit, the s
Page 183 and 184:
Note that this has the k −2 diver
Page 185 and 186:
• The effective time step, Eq. (3
Page 187 and 188:
1 2 H He 1.00794 4.00260 3 4 5 6 7
Page 189 and 190:
and the Dirac delta function is δ(
Page 191 and 192:
33.2.2 Atomic densities K eywords:
Page 193 and 194:
The spin-density matrix is a two-by
Page 195 and 196:
33.3.3 Homogeneous and isotropic sy
Page 197 and 198:
33.4 Structure factor and spherical
Page 199 and 200:
33.5 One-body density matrix, two-b
Page 201 and 202:
[ where the approximation ρ (1)T
Page 203 and 204:
The figure shows the localization l
Page 205 and 206:
with F HFT mix = − F P mix = −
Page 207 and 208:
The input keyword to activate the c
Page 209 and 210:
To each walker r j , we assign a li
Page 211 and 212:
37 Magnetic fields and the fixed-ph
Page 213 and 214:
38 Analysis of the performance of C
Page 215 and 216:
the orbitals, α = 2 [11]. The use
Page 217 and 218:
39.2 Implementation basics and perf
Page 219 and 220:
• Use ‘endif’ and ‘enddo’
Page 221 and 222:
• Evidence of testing on serial a
Page 223 and 224:
B Appendix 2: Automatic testing of
Page 225 and 226:
• Delete any eepot.data and densi
Page 227 and 228:
* "Generic" CASINO_ARCHs are intend
Page 229 and 230:
- ‘head -n 1 /etc/redhat-release
Page 231 and 232:
for a single job in an ensemble of
Page 233 and 234:
inary executable. CASINO does not r
Page 235 and 236:
otherwise. The following tags are o
Page 237 and 238:
[2] V.R. Saunders, R. Dovesi, C. Ro
Page 239 and 240:
[50] W. Janke, Statistical Analysis
show all

CASINO manual - Theory of Condensed Matter

Create successful ePaper yourself

Delete template?

Save as template?