CASINO manual - Theory of Condensed Matter

More documents

Recommendations

Info

for a given trial wave function and geometry by setting the input keyword runtype to ‘gen mpc’ and typing runqmc. One might consider using the MPC interaction because casino can evaluate it much more quickly than the Ewald interaction, and also because it gives rise to smaller finite-size effects 1 . More details are given in Sec. 19.4.4. 6.1.6 Summary of input files required by CASINO The input files (and some of the output files) required by casino are summarized in the figure below: Gaussians: correlation.data input config.in CRYSTAL95/98/03/06/09 GAUSSIAN94/98/03/09 TURBOMOLE expot.data mpc.data gwfn.data vmc.hist dmc.hist etc.. Plane waves: ABINIT CASTEP K270 GP PWSCF Numerical orbitals: TCM atomic code pwfn.data bwfn.data Blips bwfn.data.bin awfn.data dwfn.data CASINO pseudopotential file out expval.data config.out The dotted-line boxes indicate optional files, and the curved dotted line indicates that one of the wave function files defined by the arrows within the sweep of the curve must be supplied (unless you are doing a model system such as the homogeneous electron gas which does not require a trial wave function generated by an external code). A complete list of the input and output files used by casino, together with detailed information about their format, is given in Sec. 7. 6.2 How to do a VMC calculation Let’s begin by calculating the HF energy of a hydrogen atom. Change directory to ~/CASINO/examples/atom/hydrogen/. You will see a gwfn.data file generated by a gaussian94 calculation—see the bottom of gwfn.data for the gaussian output—and a casino input file (note that most casino wave function files are supplied in compressed .gz form, so you may need to gunzip them). No pseudopotential file is supplied, so casino will assume you wish to do an all-electron calculation. No correlation.data file is supplied, because the correlation energy in a one-electron atom (zero!) is not difficult to calculate without one. Look in the input file. You will see that neu and ned have been given the correct values (one spin-up electron present), periodic is F, and, as this is a finite system, the npcell block is not required. It is not necessary to equilibrate the electron distribution since there is only one electron, but vmc equil nstep is set to 500 to remind you that this should normally be done. The vmc nstep parameter is set to 100000. Note also that the runtype parameter is set to ‘vmc’, implying that we are going to perform a VMC calculation. The atom basis type parameter is set to ‘gaussian’, which means that a Gaussian basis set is used to expand the orbitals in the trial wave function. Type runqmc. Three files, out, vmc.hist and config.out, should be produced. First type envmc. This is a quick way to pull the VMC result out of the output file. It says: 1 The difference between the energy per atom obtained in a finite simulation cell and the energy per atom for an infinite crystal is smaller when the MPC interaction is used instead of the Ewald interaction. 14
ENVMC v0.60: Script to extract VMC energies from CASINO output files. Usage: envmc [-kei] [-ti] [-fisq] [-pe] [-vee] [-vei] [-vnl] [-nc] [-vr] [-rel] [-ct] [-nf ] [files] File: ./out (energies in au, variances in au) E = -0.49999(4) ; var = 0.000083(4) Total CASINO CPU time ::: 3.3700 seconds If any warnings are present in the output file, then envmc will print them out, but there shouldn’t be in this case. Note that, because of the stochastic nature of the method, the energy has an associated error bar (users of DFT, etc., may find this disconcerting!). The true HF energy of the hydrogen atom is exactly −0.5 a.u., so we have seemingly correctly performed our first VMC calculation! A point about parallel machines: if you try to run this calculation on your machine then you may get a slightly different answer. The numbers above were obtained on a single processing core; if your computer has more than one core (these days, most new machines do) and your CASINO ARCH is a parallel one, then the runqmc script will automatically detect the number of cores on your machine and run casino in parallel using that number. If you wish to reproduce the single-core result, you may use runqmc -p 1. For example, my (=MDT) personal machine has dual hex-core processors (i.e., 12 cores in total), though if I interrogate it using a command like cat /proc/cpuinfo 2> /dev/null | grep -cE "ˆprocessor" it thinks it has 24. This is because these are Intel chips with hyperthreading enabled, i.e., for each processor core that is physically present, the operating system addresses two virtual processors, and shares the workload between them when possible. This is not really useful for casino, so by default runqmc will ignore this, hence we have 12 cores. So if I execute runqmc then I get the following 12-core result: ENVMC v0.60: Script to extract VMC energies from CASINO output files. Usage: envmc [-kei] [-ti] [-fisq] [-pe] [-vee] [-vei] [-vnl] [-nc] [-vr] [-rel] [-ct] [-nf ] [files] File: ./out (energies in au, variances in au) E = -0.50000(4) ; var = 0.000088(7) Total CASINO CPU time ::: 0.4309 seconds Note the behaviour here. The second run is a lot faster but gives roughly the same error bar as the first one. This is because vmc nstep gives the total number of configuration space samples—in this case 100,000—not (as was the case with early versions of casino using the old nmove keyword) the number of samples done by each core. Giving the total number is better since it means that the input files are then independent of the number of processors on which the job is run. With 12 cores, the 100000 samples to be taken will be divided by 12 (to give 8333.333). Because this is not an integer, this number is rounded up to 8334, and so 8334×12=100008 samples will actually be done in total. Because each processor is doing less work, the calculation as a whole is much faster (not exactly 12 times faster because the setup is a significant fraction of such a short calculation). The answer will be different, however, because 12 short random walks initialized with different random number seeds sample the space differently to 1 long random walk. Next, look in the out file. We see a complete report of the calculation and at the end we see the total energy and its components. Just before the total energy, we see the ‘acceptance ratio’ which should be around 50% (the acceptance ratio depends on the VMC time step, and we have set opt dtvmc to 1 to automagically adjust the time step so that the acceptance ratio of 50% is achieved). 2 . Next, look at the file vmc.hist (see Sec. 7.10). This contains mainly energy data produced at each step of the random walk (you can average over successive steps using the vmc ave period keyword 2 If the time step is small then the electrons only attempt to move very short distances at each step of the random walk. Although the acceptance ratio is therefore high, the electrons are likely to bumble about in one corner of the configuration space, and serial correlation is likely to be significant. If the time step is large then the electrons attempt very large jumps—which are likely to be to regions of lower probability—and are thus likely to be rejected by the Metropolis algorithm. Hence the electrons don’t move very much, and the serial correlation is again large. This is the reason why an acceptance ratio of 50% usually implies nearly optimal sampling efficiency. 15
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: ATOM BASIS TYPE The basis used to r
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 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?