III.G.1.a.

Comparison of levels of theory for Si-Si

Click on an entry for a histogram of the values.
The subscript refers to how many bonds of that type have been calculated.

average calculated bond lengths (Å)

Methods with predefined basis sets
semi-empirical	AM1	1.9185 4
	PM3	2.0963 5
	PM6	1.9273 5
composite	G2	2.2101 5
	G3	2.2101 5
	G3B3	2.2649 5
	CBS-Q	2.2101 5

average calculated bond lengths (Å)

Methods with standard basis sets
		STO-3G	3-21G	3-21G*	6-31G	6-31G*	6-31G**	6-31+G**	6-311G*	6-311G**	6-31G(2df,p)	6-311+G(3df,2p)	TZVP	cc-pVDZ	cc-pVTZ	cc-pVQZ	aug-cc-pVDZ	aug-cc-pVTZ	aug-cc-pVQZ	cc-pV(T+d)Z
hartree fock	HF	2.1511 5	2.3119 5	2.2155 5	2.3026 5	2.2272 5	2.2104 5	2.2136 5	2.2138 5	2.2143 5	2.2129 5	2.2512 2	2.1689 5	2.2265 5	2.2324 5	2.2295 5	2.2473 5	2.2195 5	2.2144 5	2.2919 2
hartree fock	ROHF	2.1053 1	2.2081 1	2.2198 1	2.3142 1	2.1405 1	2.1409 1	2.2283 1	2.2307 1	2.1393 1	2.1399 1	2.2205 1		2.2352 1	2.1428 1		2.1569 1	2.1441 1
density functional	LSDA	2.2061 5	2.2179 5	2.1910 5	2.3132 5	2.2098 5	2.2101 5	2.2105 5	2.2050 5	2.2053 5	2.1996 5			2.2162 5	2.2008 5	2.1804 2	2.2170 5	2.1395 3	2.1808 2
	SVWN		2.2296 5			2.2372 3		2.1898 5
	BLYP	2.2112 5	2.3269 5	2.2278 5	2.2828 5	2.2257 5	2.2509 5	2.2517 5	2.2942 5	2.2681 5	2.2404 5	2.2998 1		2.2561 5	2.2180 5		2.2887 2
	B1B95	2.1941 5	2.2576 5	2.2309 5	2.3091 5	2.2435 5	2.2447 5	2.2458 5	2.2466 5	2.2469 5	2.2196 5			2.2551 5	2.2207 5	2.2031 3	2.2550 5	2.2091 3	2.2036 3
	B3LYP	2.2084 5	2.3032 5	2.2469 5	2.3308 5	2.2648 5	2.2419 5	2.2435 5	2.2412 5	2.2433 4	2.2357 5	2.2543 2	2.1792 5	2.2513 5	2.2592 5	2.2549 5	2.2744 5	2.2602 5	2.2335 5	2.3090 2
	B3LYPultrafine					2.2647 5						2.2670 1
	B3PW91	2.1905 4	2.2948 5	2.2399 5	2.3182 5	2.2310 5	2.2312 5	2.2553 5	2.2553 5	2.2029 4	2.2271 5	2.2597 1		2.2638 5	2.2289 5		2.2620 2
	mPW1PW91	2.1678 4	2.2898 5	2.2123 4	2.3125 5	2.2252 5	2.2478 5	2.2492 5	2.2265 5	2.2269 5	2.2433 5	2.2529 1		2.2580 5	2.2239 5		2.2581 2
	M06-2X					2.1602 5
	PBEPBE	2.1847 4	2.3109 5	2.1852 4	2.2959 4	2.2073 5	2.2323 5	2.2082 5	2.2308 5	2.2051 5	2.2239 5	2.3182 2		2.2383 5	2.2024 5	2.1577 3	2.1939 2	2.2378 3	2.1584 3	2.2860 1
	PBEPBEultrafine					2.3277 2
	HSEh1PBE					2.2152 4
Moller Plesset perturbation	MP2FC	2.2133 4	2.3748 5	2.2355 5	2.3628 5	2.2513 5	2.2326 5	2.2343 5	2.2305 5	2.2311 5	2.2365 5	2.1632 1	2.1836 5	2.2573 5	2.2544 5	2.2214 4	2.2791 5	2.2384 5	2.2744 3	2.3000 2
	MP2FU	2.2243 3	2.3757 5	2.2096 4	2.3577 4	2.2473 5	2.2283 5	2.2302 5	2.2289 5	2.2016 4	2.2030 3	2.1571 1		2.2532 5	2.2200 4	2.2143 4	2.1877 2	2.0620 1	2.2777 2	2.2833 2
	MP3					2.2275 5								2.2865 1
	MP4		2.3863 4	2.2583 1	2.4060 1	2.2627 5		2.1828 1	2.2580 2	2.2322 3		2.1765 1			2.2047 2		2.2968 1
	B2PLYP					2.1785 5		2.1798 5
Configuration interaction	CID		2.3121 4	2.1990 4	2.3389 4	2.2209 5		2.2500 1	2.2189 5			2.2378 1		2.2704 1	2.1545 1
Configuration interaction	CISD		2.3158 4	2.2025 4	2.3416 4	2.2240 5	2.1615 1	2.2527 1	2.2051 3			2.2400 1		2.2730 1	2.1578 1
Quadratic configuration interaction	QCISD		2.3483 5	2.2142 4	2.3607 4	2.2530 5	2.2210 3	2.2370 5	2.2331 5	2.2523 5	2.2201 3	2.1638 1		2.2629 5	2.2278 4		2.2824 1			2.2489 1
Quadratic configuration interaction	QCISD(T)					2.2439 5		2.2715 1	2.3059 2			2.2614 1		2.2743 4	2.2215 4		2.2570 4	2.2378 3
Coupled Cluster	CCD		2.3533 3	2.2073 4	2.3548 4	2.2477 5	2.2130 3	2.2026 4	2.2265 5	2.2109 3	2.2134 3	2.1566 1		2.2577 5	2.2220 4		2.2559 4	2.2157 3
	CCSD					2.1783 4		2.2597 1	2.2993 2			2.2475 1		2.2817 1	2.1675 1		2.1988 1
	CCSD(T)		2.4145 1			2.2697 4	2.2598 2	2.2706 1	2.3054 2	2.2705 1		2.2607 1		2.2731 4	2.2465 5	2.0861 1	2.2557 4	2.2367 3		2.2624 1
	CCSD(T)=FULL					2.2268 3										2.0750 1

average calculated bond lengths (Å)

Methods with effective core potentials (select basis sets)
		CEP-31G	CEP-31G*	CEP-121G	CEP-121G*	LANL2DZ	SDD
hartree fock	HF	2.3313 5	2.2492 5	2.3707 5	2.2543 5	2.3292 5	2.3159 5
density functional	B1B95	2.3853 2	2.3311 2
density functional	B3LYP	2.4262 5	2.3016 5	2.4249 5	2.2982 5	2.3836 5	2.3417 5
Moller Plesset perturbation	MP2FC	2.4571 5	2.2783 5	2.4532 5	2.2852 5	2.4087 5	2.3771 5

For descriptions of the methods (AM1, HF, MP2, ...) and basis sets (3-21G, 3-21G*, 6-31G, ...) see the glossary in section I.C. Predefined means the basis set used is determined by the method.