1% 2% $Id$ 3% 4\label{sec:oniom} 5 6ONIOM is the hybrid method of Morokuma and co-workers that enables 7different levels of theory to be applied to different parts of a 8molecule/system and combined to produce a consistent energy 9expression. The objective is to perform a high-level calculation on 10just a small part of the system and to include the effects of the 11remainder at lower levels of theory, with the end result being of 12similar accuracy to a high-level calculation on the full system. 13 14\begin{enumerate} 15\item M. Svensson, S. Humbel, R.D.J. Froese, T. Mastubara, S. Sieber, and 16K. Morokuma, J.~Phys.~Chem., 100, 19357 (1996). 17\item S. Dapprich, I. Komaromi, K.S. Byun, K. Morokuma, and M.J. Frisch, 18J.~Mol.~Struct.~(Theochem), 461-462, 1 (1999). 19\item R.D.J. Froese and K. Morokuma in ``Encylopedia of Computational Chemistry,'' 20volume 2, pp.1244-1257, (ed. P. von Rague Schleyer, John Wiley and Sons, 21Chichester, Sussex, 1998). 22\end{enumerate} 23 24The NWChem ONIOM module implements two- and three-layer ONIOM models 25for use in energy, gradient, geometry optimization, and vibrational 26frequency calculations with any of the pure quantum mechanical methods 27within NWChem. At the present time, it is not possible to perform 28ONIOM calculations with either solvation models or classical force 29fields. Nor is it yet possible to compute properties except as 30derivatives of the total energy. 31 32Using the terminology of Morokuma et al., the full molecular geometry 33including all atoms is referred to as the ``real'' geometry and it is 34treated using a ``low''-level of theory. A subset of these atoms 35(referred to as the ``model'' geometry) are treated using both the 36``low''-level and a ``high''-level of theory. A three-layer model 37also introduces an ``intermediate'' model geometry and a ``medium'' 38level of theory. 39 40The two-layer model requires a high and low level of theory and a 41real and model molecular geometry. The energy at the high-level of 42theory for the real geometry is estimated as 43\begin{verbatim} 44 E(High,Real) = E(Low,Real) + [E(High,Model) - E(Low,Model)]. 45\end{verbatim} 46The three-layer model requires high, medium and low levels of theory, 47and real, intermediate and model geometries and the corresponding 48energy estimate is 49\begin{verbatim} 50 E(High,Real) = E(Low,Real) + [E(High,Model) - E(Medium,Model)] 51 + [E(Medium,Inter) - E(Low,Inter)]. 52\end{verbatim} 53 54When does ONIOM work well? The approximation for a two-layer model 55will be good if 56\begin{itemize} 57\item the model system includes the interactions that dominate the 58 energy difference being computed and the high-level of theory 59 describes these to the required precision, and 60\item the interactions between the model and the rest of the real system 61 (substitution effects) are described to sufficient accuracy at the 62 lower level of theory. 63\end{itemize} 64ONIOM is used to compute energy differences and the absolute energies 65are not all that meaningful even though they are well defined. Due to 66cancellation of errors, ONIOM actually works better than you might 67expect, but a poorly designed calculation can yield very bad results. 68Please read and heed the caution at the end of the article by Dapprich 69et al. 70 71The input options are as follows 72\begin{verbatim} 73ONIOM 74 HIGH <string theory> [basis <string basis default "ao basis">] \ 75 [ecp <string ecp>] [input <string input>] 76 [MEDIUM <string theory> [basis <string basis default "ao basis">] \ 77 [ecp <string ecp>] [input <string input>]] 78 LOW <string theory> [basis <string basis default "ao basis">] \ 79 [ecp <string ecp>] [input <string input>] 80 MODEL <integer natoms> [charge <double charge>] \ 81 [<integer i1 j1> <real g1> [<string tag1>] ...] 82 [INTER <integer natoms> [charge <double charge>] \ 83 [<integer i1 j1> <real g1> [<string tag1>] ...]] 84 [VECTORS [low-real <string mofile>] [low-model <string mofile>] \ 85 [high-model <string mofile>] [medium-model <string mofile]\ 86 [medium-inter <string mofile>] [low-inter <string mofile>]] 87 [PRINT ...] 88 [NOPRINT ...] 89END 90\end{verbatim} 91which are described in detail below. 92 93{\em For better validation of user input, the \verb+HIGH+, 94\verb+LOW+ and \verb+MODEL+ directives must always be specified. If 95the one of the \verb+MEDIUM+ or \verb+INTER+ directives are specified, 96then so must the other.} 97 98\section{Real, model and intermediate geometries} 99 100The geometry and total charge of the full or real system should be 101specified as normal using the geometry directive (see Section 102\ref{sec:geom}). If $N_{model}$ of the atoms are to be included in 103the model system, then these should be specified first in the 104geometry. Similarly, in a three-layer calculation, if there are 105$N_{inter}$ atoms to be included in the intermediate system, then 106these should also be arranged together at the beginning of the 107geometry. The implict assumption is that the model system is a subset 108of the intermediate system which is a subset of the real system. The 109number of atoms to be included in the model and intemediate systems 110are specified using the \verb+MODEL+ and \verb+INTER+ directives. 111Optionally, the total charge of the model and intermediate systems may 112be adjusted. The default is that all three systems have the same 113total charge. 114 115Example 1. A two-layer calculation on $K^{+}(H_2O)$ taking the 116potassium ion as the model system. Note that no bonds are broken so 117no link atoms are introduced. The real geometry would be specified 118with potassium (the model) first. 119\begin{verbatim} 120 geometry autosym 121 K 0 0.00 1.37 122 O 0 0.00 -1.07 123 H 0 -0.76 -1.68 124 H 0 0.76 -1.68 125 end 126\end{verbatim} 127and the following directive in the ONIOM input block indicates that 128one atom (implicitly the first in the geometry) is in the model system 129\begin{verbatim} 130 model 1 131\end{verbatim} 132 133\subsection{Link atoms} 134Link atoms for bonds spanning two regions are automatically generated 135from the bond information. The additional parameters on the 136\verb+MODEL+ and \verb+INTER+ directives describe the broken bonds 137including scale factors for placement of the link atom 138and, optionally, the type of link atom. The type of link atom 139defaults to hydrogen, but any type may be specified (actually here you 140are specifying a geometry tag which is used to associate a geometrical 141center with an atom type and basis sets, etc.. See section 142\ref{sec:cart}). 143For each broken bond specify the numbers of the two atoms (i and j), 144the scale factor (g) and optionally the tag of the link atom. Link 145atoms are placed along the vector connecting the the first to the 146second atom of the bond according to the equation 147\begin{displaymath} 148\underline{R}_{link} = (1-g)\underline{R}_{1} + g*\underline{R}_{2} 149\end{displaymath} 150where $g$ is the scale factor. If the scale factor is one, then the 151link atom is placed where the second atom was. More usually, the 152scale factor is less than one, in which case the link atom is placed 153between the original two atoms. The scale factor should be chosen so 154that the link atom (usually hydrogen) is placed near its equilibrium 155bond length from the model atom. E.g., when breaking a single 156carbon-carbon bond (typical length 1.528 {\angstroms}) using a hydrogen 157link atom we will want a carbon-hydrogen bond length of about 1.084 158{\angstroms}, so the scale factor should be chosen as $1.084/1.528 159\approx 0.709$. 160 161Example 2. A calculation on acetaldehyde ($H_3C-CHO$) using aldehyde 162($H-CHO$) as the model system. The covalent bond between the two 163carbon atoms is broken and a link atom must be introduced to replace 164the methyl group. The link atom is automatically generated --- all 165you need to do is specify the atoms in the model system that are also 166in the real system (here $CHO$) and the broken bonds. Here is the 167geometry of acetaldehyde with the $CHO$ of aldehyde first 168\begin{verbatim} 169 geometry 170 C -0.383 0.288 0.021 171 H -1.425 0.381 0.376 172 O 0.259 1.263 -0.321 173 174 H 0.115 -1.570 1.007 175 H -0.465 -1.768 -0.642 176 H 1.176 -1.171 -0.352 177 C 0.152 -1.150 0.005 178 end 179\end{verbatim} 180There are three atoms (the first three) of the real geometry included 181in the model geometry, and we are breaking the bond between atoms 1 182and 7, replacing atom 7 with a hydrogen link atom. This is all 183accomplished by the directive 184\begin{verbatim} 185 model 3 1 7 0.709 H 186\end{verbatim} 187Since the default link atom is hydrogen there is actually no need to 188specify the ``H''. 189 190See also Section \ref{sec:oniomeg3} for a more complex example. 191 192\subsection{Numbering of the link atoms} 193 194The link atoms are appended to the atoms of the model or intermediate 195systems in the order that the broken bonds are specified in the input. 196This is of importance only if manually constructing an initial guess. 197 198\section{High, medium and low theories} 199 200The two-layer model requires both the high-level and low-level 201theories be specified. The three-layer model also requires the 202medium-level theory. Each of these includes a theory (such as SCF, 203MP2, DFT, CCSD, CCSD(T), etc.), an optional basis set, an optional ECP, 204and an optional string containing general NWChem input. 205 206\subsection{Basis specification} 207The basis name on the theory directive (high, medium, or low) is that 208specified on a basis set directive (see Section \ref{sec:basis}) and 209{\em not} the name of a standard basis in the library. If not 210specified, the basis set for the high-level theory defaults to the 211standard \verb+"ao basis"+. That for the medium level defaults to the 212high-level basis, and the low-level basis defaults to the medium-level 213basis. Other wavefunction parameters are obtained from the standard 214wavefunction input blocks. See \ref{sec:oniomeg2} for an example. 215 216\subsection{Effective core potentials} 217 218If an effective core potential is specified in the usual fashion (see 219Section \ref{sec:ecp}) outside of the ONIOM input then this will be 220used in all calculations. If an alternative ECP name (the name 221specified on the ECP directive in the same manner as done for basis 222sets) is specified on one of the theory directives, then this ECP will 223be used in preference for that level of theory. See Section 224\ref{sec:oniomeg2} for sample input. 225 226\subsection{General input strings} 227 228For many purposes, the ability to specify the theory, basis and 229effective core potential is adequate. All of the options for each 230theory are determined from their independent input blocks. However, 231if the same theory (e.g., DFT) is to be used with different options 232for the ONIOM theoretical models, then the general input strings must 233be used. These strings are processed as NWChem input each time the 234theoretical model is invoked. The strings may contain any NWChem 235input, except for options pertaining to ONIOM and the task directive. 236The intent that the strings be used just to control the options 237pertaining to the theory being used. 238 239A word of caution. Be sure to check that the options are producing 240the desired results. Since the NWChem database is persistent and the 241ONIOM calculations happen in an undefined order, the input strings 242should fully define the calculation you wish to have happen. 243 244For instance, if the high model is DFT/B3LYP/6-311g** and the 245low model is DFT/LDA/3-21g, the ONIOM input might look like this 246\begin{verbatim} 247 oniom 248 model 3 249 low dft basis 3-21g input "dft\; xc\; end" 250 high dft basis 6-311g** input "dft\; xc b3lyp\; end" 251 end 252\end{verbatim} 253The empty \verb+XC+ directive restores the default LDA 254exchange-correlation option (see Section \ref{sec:xc}). Note that 255semi-colons and other quotation marks inside the input string must be 256preceded by a backslash to avoid special interpretation. 257 258See Section \ref{sec:oniomeg4} for another example. 259 260\section{Use of symmetry} 261 262Symmetry should work just fine as long as the model and intermediate 263regions respect the symmetry --- i.e., symmetry equivalent atoms need 264to be treated equivalently. If symmetry equivalent atoms must be 265treated in separate regions then the symmetry must be lowered (or 266completely switched off). 267 268\section{Molecular orbital files} 269 270The \verb+VECTORS+ directive in the ONIOM block is different to that 271elsewhere in NWChem. For each of the necessary combinations of theory 272and geometry you can specify a different file for the molecular 273orbitals. By default each combination will store the MO vectors in 274the permanent directory using a file name created by appending to the 275name of the calculation the following string 276\begin{itemize} 277\item low-real --- \verb+".lrmos"+ 278\item low-inter --- \verb+".limos"+ 279\item low-model --- \verb+".lmmos"+ 280\item medium-inter --- \verb+".mimos"+ 281\item medium-model --- \verb+".mmmos"+ 282\item high-model --- \verb+".hmmos"+ 283\end{itemize} 284Each calculation will utilize the appropriate vectors which is more 285efficient during geometry optimizations and frequency calculations, 286and is also useful for the initial calculation. In the absence of 287existing MO vectors files, the default atomic guess is used (see 288Section \ref{sec:vectors}). 289 290If special measures must be taken to converge the initial SCF, DFT or 291MCSCF calculation for one or more of the systems, then initial vectors 292may be saved in a file with the default name, or another name may be 293specified using the \verb+VECTORS+ directive. Note that subsequent 294vectors (e.g., from a geometry optimization) will be written back to 295this file, so take a copy if you wish to preserve it. 296To generate the initial guess for the model or intermediate systems 297it is necessary to generate the geometries which is most readily 298done, if there are link atoms, by just running NWChem on the 299input for the ONIOM calculation on your workstation. It will 300print these geometries before starting any calculations which 301you can then terminate. 302 303E.g., in a calculation on Fe(III) surrounded by some ligands, it is 304hard to converge the full (real) system from the atomic guess so as to 305obtain a $d^5$ configuration for the iron atom since the $d$ orbitals 306are often nominally lower in energy than some of the ligand orbitals. 307The most effective mechanism is to converge the isolated Fe(III) and 308then to use the fragment guess (see Section \ref{sec:fragguess}) as a 309starting guess for the real system. The resulting converged molecular 310orbitals can be saved either with the default name (as described above 311in this section), in which case no additional input is necessary. If 312an alternative name is desired, then the \verb+VECTORS+ directive may 313be used as follows 314\begin{verbatim} 315 vectors low-real /u/rjh/jobs/fe_ether_water.mos 316\end{verbatim} 317 318\section{Restarting} 319 320Restart of ONIOM calculations does not currently work as smoothly as 321we would like. For geometry optimizations that terminated gracefully 322by running out of iterations, the restart will work as normal. 323Otherwise, specify in the input of the restart job the last geometry 324of the optimization. The Hessian information will be reused and the 325calculation should proceed losing at most the cost of one ONIOM 326gradient evaluation. For energy or frequency calculations, restart 327may not currently be possible. 328 329\section{Examples} 330 331\subsection{Hydrocarbon bond energy} 332\label{sec:oniomeg1} 333 334A simple two-layer model changing just the wavefunction with one 335link atom. 336 337This reproduces the two-layer ONIOM (MP2:HF) result from Dapprich et 338al.\ for the reaction $R-CH_3 = R-CH_2 + H$ with $R=CH_3$ using $CH_4$ 339as the model . The geometries of $R-CH_3$ and $R-CH_2$ are optimized 340at the DFT-B3LYP/6-311++G** level of theory, and then ONIOM is used to 341compute the binding energy using UMP2 for the model system and HF for 342the real system. The results, including MP2 calculations on the full 343system for comparison, are as given in Table \ref{tab:oniom1} 344 345\begin{table}[h] 346\begin{center} 347\begin{tabular}{lccccc} 348 Theory & Me-CH2 & Me-Me & H & De(Hartree)& De(kcal/mol) \\ \hline 349 B3LYP & -79.185062& -79.856575& -0.502256& 0.169257 & 106.2 \\ 350 HF & -78.620141& -79.251701& -0.499817& 0.131741 & 82.7 \\ 351 MP2 & -78.904716& -79.571654& -0.499817& 0.167120 & 104.9 \\ 352 MP2:HF & -78.755223& -79.422559& -0.499817& 0.167518 & 105.1 \\ \hline 353\end{tabular} 354\caption{\label{tab:oniom1} Energies for ONIOM example 1, hydrocarbon bond energy using MP2:HF two-layer model.} 355\end{center} 356\end{table} 357 358The following input first performs a calculation on $CH_3-CH_2$, and then 359on $CH_3-CH_3$. Note that in the second calculation we cannot use the 360full symmetry since we are breaking the C-C bond in forming the model 361system (the non-equivalence of the methyl groups is perhaps more 362apparent if we write $R-CH_3$). 363 364\begin{verbatim} 365 start 366 367 basis spherical 368 H library 6-311++G**; C library 6-311++G** 369 end 370 371 title "ONIOM Me-CH2" 372 373 geometry autosym 374 H -0.23429328 1.32498565 0.92634814 375 H -0.23429328 1.32498565 -0.92634814 376 C -0.13064265 0.77330370 0.00000000 377 H -1.01618703 -1.19260361 0.00000000 378 H 0.49856072 -1.08196901 -0.88665533 379 H 0.49856072 -1.08196901 0.88665533 380 C -0.02434414 -0.71063687 0.00000000 381 end 382 383 scf; uhf; doublet; thresh 1e-6; end 384 mp2; freeze atomic; end 385 386 oniom 387 high mp2 388 low scf 389 model 3 3 7 0.724 390 end 391 392 task oniom 393 394 title "ONIOM Me-Me" 395 396 geometry # Note cannot use full D3D symmetry here 397 H -0.72023641 0.72023641 -1.16373235 398 H 0.98386124 0.26362482 -1.16373235 399 H -0.26362482 -0.98386124 -1.16373235 400 C 0.00000000 0.00000000 -0.76537515 401 H 0.72023641 -0.72023641 1.16373235 402 H -0.98386124 -0.26362482 1.16373235 403 H 0.26362482 0.98386124 1.16373235 404 C 0.00000000 0.00000000 0.76537515 405 end 406 407 scf; rhf; singlet; end 408 409 oniom 410 high mp2 411 low scf 412 model 4 4 8 0.724 413 end 414 415 task oniom 416\end{verbatim} 417 418\subsection{Optimization and frequencies} 419\label{sec:oniomeg2} 420A two-layer model including modification of theory, basis, ECP and 421total charge and no link atoms. 422 423This input reproduces the ONIOM optimization and vibrational frequency 424calculation of $Rh(CO)_2Cp$ of Dapprich et al. The model system is 425$Rh(CO)_2^+$. The low theory is the Gaussian LANL2MB model (Hay-Wadt 426n+1 ECP with minimal basis on Rh, STO-3G on others) with SCF. The 427high theory is the Gaussian LANL2DZ model (another Hay-Wadt ECP with a 428DZ basis set on Rh, Dunning split valence on the other atoms) with 429DFT/B3LYP. Note that different names should be used for the basis set 430and ECP since the same mechanism is used to store them in the 431database. 432 433\begin{verbatim} 434 start 435 436 ecp LANL2DZ_ECP 437 rh library LANL2DZ_ECP 438 end 439 440 basis LANL2DZ spherical 441 rh library LANL2DZ_ECP 442 o library SV_(Dunning-Hay); c library SV_(Dunning-Hay); h library SV_(Dunning-Hay) 443 end 444 445 ecp Hay-Wadt_MB_(n+1)_ECP 446 rh library Hay-Wadt_MB_(n+1)_ECP 447 end 448 449 # This is the minimal basis used by Gaussian. It is not the same 450 # as the one in the EMSL basis set library for this ECP. 451 basis Hay-Wadt_MB_(n+1) spherical 452 Rh s; .264600D+01 -.135541D+01; .175100D+01 .161122D+01; .571300D+00 .589381D+00 453 Rh s; .264600D+01 .456934D+00; .175100D+01 -.595199D+00; .571300D+00 -.342127D+00 454 .143800D+00 .410138D+00; .428000D-01 .780486D+00 455 Rh p; .544000D+01 -.987699D-01; .132900D+01 .743359D+00; .484500D+00 .366846D+00 456 Rh p; .659500D+00 -.370046D-01; .869000D-01 .452364D+00; .257000D-01 .653822D+00 457 Rh d; .366900D+01 .670480D-01; .142300D+01 .455084D+00; .509100D+00 .479584D+00 458 .161000D+00 .233826D+00 459 o library sto-3g; c library sto-3g; h library sto-3g 460 end 461 462 charge 0 463 geometry autosym 464 rh 0.00445705 -0.15119674 0.00000000 465 c -0.01380554 -1.45254070 1.35171818 466 c -0.01380554 -1.45254070 -1.35171818 467 o -0.01805883 -2.26420212 2.20818932 468 o -0.01805883 -2.26420212 -2.20818932 469 c 1.23209566 1.89314720 0.00000000 470 c 0.37739392 1.84262319 -1.15286640 471 c -1.01479160 1.93086461 -0.70666350 472 c -1.01479160 1.93086461 0.70666350 473 c 0.37739392 1.84262319 1.15286640 474 h 2.31251453 1.89903673 0.00000000 475 h 0.70378132 1.86131979 -2.18414218 476 h -1.88154273 1.96919306 -1.35203550 477 h -1.88154273 1.96919306 1.35203550 478 h 0.70378132 1.86131979 2.18414218 479 end 480 481 dft; grid fine; convergence gradient 1e-6 density 1e-6; xc b3lyp; end 482 scf; thresh 1e-6; end 483 484 oniom 485 low scf basis Hay-Wadt_MB_(n+1) ecp Hay-Wadt_MB_(n+1)_ECP 486 high dft basis LANL2DZ ecp LANL2DZ_ECP 487 model 5 charge 1 488 print low 489 end 490 491 task oniom optimize 492 task oniom freq 493\end{verbatim} 494 495\subsection{A three-layer example} 496\label{sec:oniomeg3} 497 498A three layer example combining CCSD(T), and MP2 with two different 499quality basis sets, and using multiple link atoms. 500 501The full system is tetra-dimethyl-amino-ethylene (TAME) or 502(N(Me)2)2-C=C-(N(Me)2)2. The intermediate system is (NH2)2-C=C-(NH2)2 503and H2C=CH2 is the model system. CCSD(T)+aug-cc-pvtz is used for the 504model region, MP2+aug-cc-pvtz for the intermediate region, and 505MP2+aug-cc-pvdz for everything. 506 507In the real geometry the first two atoms (C, C) are the model system 508(link atoms will be added automatically). The first six atoms (C, C, 509N, N, N, N) describe the intermediate system (again with link atoms to 510be added automatically). The atoms have been numbered using comments 511to make the bonding input easier to generate. 512 513To make the model system, four C-N bonds are broken between the 514ethylene fragment and the dimethyl-amino groups and replaced with C-H 515bonds. To make the intermediate system, eight C-N bonds are broken 516between the nitrogens and the methyl groups and replaced with N-H 517bonds. The scaling factor could be chosen differently for each of the 518bonds. 519 520\begin{verbatim} 521 start 522 523 geometry 524 C 0.40337795 -0.17516305 -0.51505208 # 1 525 C -0.40328664 0.17555927 0.51466084 # 2 526 N 1.87154979 -0.17516305 -0.51505208 # 3 527 N -0.18694782 -0.60488524 -1.79258692 # 4 528 N 0.18692927 0.60488318 1.79247594 # 5 529 N -1.87148219 0.17564718 0.51496494 # 6 530 C 2.46636552 1.18039452 -0.51505208 # 7 531 C 2.48067731 -1.10425355 0.46161675 # 8 532 C -2.46642715 -1.17982091 0.51473105 # 9 533 C -2.48054940 1.10495864 -0.46156202 # 10 534 C 0.30027136 0.14582197 -2.97072148 # 11 535 C -0.14245927 -2.07576980 -1.96730852 # 12 536 C -0.29948109 -0.14689874 2.97021079 # 13 537 C 0.14140463 2.07558249 1.96815181 # 14 538 H 0.78955302 2.52533887 1.19760764 539 H -0.86543435 2.50958894 1.88075113 540 ... and 22 other hydrogen atoms on the methyl groups 541 end 542 543 basis aug-cc-pvtz spherical 544 C library aug-cc-pvtz; H library aug-cc-pvtz 545 end 546 547 basis aug-cc-pvdz spherical 548 C library aug-cc-pvtz; H library aug-cc-pvtz 549 end 550 551 oniom 552 high ccsd(t) basis aug-cc-pvtz 553 medium mp2 basis aug-cc-pvtz 554 low mp2 basis aug-cc-pvdz 555 model 2 1 3 0.87 1 4 0.87 2 5 0.87 2 6 0.87 556 557 inter 6 3 7 0.69 3 8 0.69 4 11 0.69 4 12 0.69 \ 558 5 13 0.69 5 14 0.69 6 9 0.69 6 10 0.69 559 end 560 561 task oniom 562\end{verbatim} 563 564\subsection{DFT with and without charge fitting} 565\label{sec:oniomeg4} 566Demonstrates use of general input strings. 567 568A two-layer model for anthracene (a linear chain of three fused benzene 569rings) using benzene as the model system. The high-level theory is 570DFT/B3LYP/TZVP with exact Coulomb. The low level is DFT/LDA/DZVP2 with 571charge fitting. 572 573Note the following. 574\begin{enumerate} 575\item The semi-colons and quotation marks inside the input string must be 576quoted with backslash. 577\item The low level of theory sets the fitting basis set and the high level of 578theory unsets it. 579\end{enumerate} 580 581\begin{verbatim} 582 start 583 geometry 584 symmetry d2h 585 C 0.71237329 -1.21458940 0.0 586 C -0.71237329 -1.21458940 0.0 587 C 0.71237329 1.21458940 0.0 588 C -0.71237329 1.21458940 0.0 589 C -1.39414269 0.00000000 0.0 590 C 1.39414269 0.00000000 0.0 591 H -2.47680865 0.00000000 0.0 592 H 2.47680865 0.00000000 0.0 593 C 1.40340535 -2.48997027 0.0 594 C -1.40340535 -2.48997027 0.0 595 C 1.40340535 2.48997027 0.0 596 C -1.40340535 2.48997027 0.0 597 C 0.72211503 3.64518615 0.0 598 C -0.72211503 3.64518615 0.0 599 C 0.72211503 -3.64518615 0.0 600 C -0.72211503 -3.64518615 0.0 601 H 2.48612947 2.48094825 0.0 602 H 1.24157357 4.59507342 0.0 603 H -1.24157357 4.59507342 0.0 604 H -2.48612947 2.48094825 0.0 605 H 2.48612947 -2.48094825 0.0 606 H 1.24157357 -4.59507342 0.0 607 H -1.24157357 -4.59507342 0.0 608 H -2.48612947 -2.48094825 0.0 609 end 610 611 basis small 612 h library DZVP_(DFT_Orbital) 613 c library DZVP_(DFT_Orbital) 614 end 615 616 basis fitting 617 h library DGauss_A1_DFT_Coulomb_Fitting 618 c library DGauss_A1_DFT_Coulomb_Fitting 619 end 620 621 basis big 622 h library TZVP_(DFT_Orbital) 623 c library TZVP_(DFT_Orbital) 624 end 625 626 oniom 627 model 8 1 9 0.75 2 10 0.75 3 11 0.75 4 12 0.75 628 high dft basis big input "unset \"cd basis\"\; dft\; xc b3lyp\; end" 629 low dft basis small input "set \"cd basis\" fitting\; dft\; xc\; end" 630 end 631 632 task oniom 633\end{verbatim} 634