CCCBDB calculation results Page

State	Conformation	minimum conformation	conformer description	state description
1	1	yes	D2H	¹A_g
1	2	no	D4H	¹A_1g

Conformer 1 (D2H)

Jump to S1C2

Energy calculated at HF/daug-cc-pVTZ

	hartrees
Energy at 0K	-153.699175
Energy at 298.15K	-153.702539
HF Energy	-153.699175
Nuclear repulsion energy	99.876989

The energy at 298.15K was derived from the energy at 0K and an integrated heat capacity that used the calculated vibrational frequencies.

Vibrational Frequencies calculated at HF/daug-cc-pVTZ

Mode Number	Symmetry	Frequency (cm^-1)	Scaled Frequency (cm^-1)	IR Intensities (km mol^-1)
1	A_g	3402	3077	0.00
2	A_g	1746	1579	0.00
3	A_g	1206	1091	0.00
4	A_g	1024	927	0.00
5	A_u	1014	917	0.00
6	A_u	597	540	0.00
7	B_1g	1015	918	0.00
8	B_1u	3391	3068	11.39
9	B_1u	1767	1599	15.92
10	B_1u	1149	1039	0.01
11	B_2g	703	636	0.00
12	B_2u	3368	3047	8.81
13	B_2u	1392	1259	41.90
14	B_2u	802	725	14.55
15	B_3g	3352	3032	0.00
16	B_3g	1298	1174	0.00
17	B_3g	923	835	0.00
18	B_3u	675	611	176.59

Unscaled Zero Point Vibrational Energy (zpe) 14411.0 cm^-1
Scaled (by 0.9046) Zero Point Vibrational Energy (zpe) 13036.2 cm^-1
See section III.C.1 List or set vibrational scaling factors to change the scale factors used here.
See section III.C.2 Calculate a vibrational scaling factor for a given set of molecules to determine the least squares best scaling factor.

Rotational Constants (cm^-1) from geometry optimized at HF/daug-cc-pVTZ

A	B	C
0.58413	0.43429	0.24909

See section I.F.4 to change rotational constant units

Geometric Data calculated at HF/daug-cc-pVTZ

Point Group is D_2h

Cartesians (Å)

Atom	y (Å)	z (Å)
C1	0.658	0.781
C2	0.658	-0.781
C3	-0.658	0.781
C4	-0.658	-0.781
H5	1.416	1.536
H6	1.416	-1.536
H7	-1.416	1.536
H8	-1.416	-1.536

Atom - Atom Distances (Å)

	C1	C2	C3	C4	H5	H6	H7	H8
C1		1.5626	1.3158	2.0428	1.0699	2.4385	2.2070	3.1101
C2	1.5626		2.0428	1.3158	2.4385	1.0699	3.1101	2.2070
C3	1.3158	2.0428		1.5626	2.2070	3.1101	1.0699	2.4385
C4	2.0428	1.3158	1.5626		3.1101	2.2070	2.4385	1.0699
H5	1.0699	2.4385	2.2070	3.1101		3.0728	2.8319	4.1787
H6	2.4385	1.0699	3.1101	2.2070	3.0728		4.1787	2.8319
H7	2.2070	3.1101	1.0699	2.4385	2.8319	4.1787		3.0728
H8	3.1101	2.2070	2.4385	1.0699	4.1787	2.8319	3.0728

picture of cyclobutadiene state 1 conformation 1

More geometry information
Calculated Bond Angles

atom1	atom2	atom3	angle	atom1	atom2	atom3	angle
C1	C2	C4	90.000	C1	C2	H6	134.890
C1	C3	C4	90.000	C1	C3	H7	135.110
C2	C1	C3	90.000	C2	C1	H5	134.890
C2	C4	C3	90.000	C3	C1	H5	135.110
C4	C2	H6	135.110	C4	C3	H7	134.890

Electronic energy levels

Charges, Dipole, Quadrupole and Polarizability
Charges from optimized geometry at HF/daug-cc-pVTZ Charges (e)

Number	Element	Mulliken
1	C	-0.819
2	C	-0.819
3	C	-0.819
4	C	-0.819
5	H	0.819
6	H	0.819
7	H	0.819
8	H	0.819

Electric dipole moments
Electric dipole components in Debye
(What's a Debye? See section VII.A.3)

	x	y	z	Total
	0.000	0.000	0.000	0.000
CHELPG
AIM
ESP

Electric Quadrupole moment
Quadrupole components in D Å

Primitive
	x	y	z
x	-27.426	0.000	0.000
y	0.000	-20.637	0.000
z	0.000	0.000	-22.769

Traceless
	x	y	z
x	-5.724	0.000	0.000
y	0.000	4.461	0.000
z	0.000	0.000	1.263

Polar
3z²-r²	2.526
x²-y²	-6.789
xy	0.000
xz	0.000
yz	0.000

Polarizabilities
Components of the polarizability tensor.
Units are Å³ (Angstrom cubed)
Change units.

	x	y	z
x	4.970	0.000	0.000
y	0.000	7.672	0.000
z	0.000	0.000	6.942

<r²> (average value of r²) Å²

<r²>	57.247
(<r²>)^1/2	7.566

Conformer 2 (D4H)

Jump to S1C1

Energy calculated at HF/daug-cc-pVTZ

	hartrees
Energy at 0K	-153.648507
Energy at 298.15K
HF Energy	-153.648507
Nuclear repulsion energy	100.491418

The energy at 298.15K was derived from the energy at 0K and an integrated heat capacity that used the calculated vibrational frequencies.

Vibrational Frequencies calculated at HF/daug-cc-pVTZ

Mode Number	Symmetry	Frequency (cm^-1)	Scaled Frequency (cm^-1)	IR Intensities (km mol^-1)
1	A_g	3474	3143	0.00
2	A_g	3308	2993	0.00
3	A_g	1368	1237	0.00
4	A_g	1033	935	0.00
5	B_1g	1218	1102	0.00
6	B_1u	3464	3134	20.33
7	B_1u	1564	1415	140.62
8	B_1u	1026	928	237.85
9	B_2g	427i	387i	0.00
10	B_2u	3314	2998	50.47
11	B_2u	1399	1265	174.25
12	B_2u	1036	938	27.14
13	B_3g	7509	6792	0.00
14	B_3g	1326	1200	0.00
15	B_3g	1139	1030	0.00
16	B_3u	1064	963	3.01
17	B_3u	601	543	150.30
18	B_3u	375i	339i	196.29

Unscaled Zero Point Vibrational Energy (zpe) 16520.1 cm^-1
Scaled (by 0.9046) Zero Point Vibrational Energy (zpe) 14944.1 cm^-1
See section III.C.1 List or set vibrational scaling factors to change the scale factors used here.
See section III.C.2 Calculate a vibrational scaling factor for a given set of molecules to determine the least squares best scaling factor.

Rotational Constants (cm^-1) from geometry optimized at HF/daug-cc-pVTZ

A	B	C
0.55381	0.47379	0.25534

See section I.F.4 to change rotational constant units

Geometric Data calculated at HF/daug-cc-pVTZ

Point Group is D_2h

Cartesians (Å)

Atom	y (Å)	z (Å)
C1	0.959	0.000
C2	0.000	1.052
C3	0.000	-1.052
C4	-0.959	0.000
H5	2.037	0.000
H6	0.000	2.114
H7	0.000	-2.114
H8	-2.037	0.000

Atom - Atom Distances (Å)

	C1	C2	C3	C4	H5	H6	H7	H8
C1		1.4238	1.4238	1.9182	1.0776	2.3212	2.3212	2.9958
C2	1.4238		2.1046	1.4238	2.2925	1.0615	3.1660	2.2925
C3	1.4238	2.1046		1.4238	2.2925	3.1660	1.0615	2.2925
C4	1.9182	1.4238	1.4238		2.9958	2.3212	2.3212	1.0776
H5	1.0776	2.2925	2.2925	2.9958		2.9353	2.9353	4.0734
H6	2.3212	1.0615	3.1660	2.3212	2.9353		4.2275	2.9353
H7	2.3212	3.1660	1.0615	2.3212	2.9353	4.2275		2.9353
H8	2.9958	2.2925	2.2925	1.0776	4.0734	2.9353	2.9353

picture of cyclobutadiene state 1 conformation 2

More geometry information
Calculated Bond Angles

atom1	atom2	atom3	angle	atom1	atom2	atom3	angle
C1	C2	C4	84.697	C1	C2	H6	137.652
C1	C3	C4	84.697	C1	C3	H7	137.652
C2	C1	C3	95.303	C2	C1	H5	132.348
C2	C4	C3	95.303	C3	C1	H5	132.348
C4	C2	H6	137.652	C4	C3	H7	137.652

Electronic energy levels

Charges, Dipole, Quadrupole and Polarizability
Charges from optimized geometry at HF/daug-cc-pVTZ Charges (e)

Number	Element	Mulliken
1	C	0.250
2	C	-1.912
3	C	-1.912
4	C	0.250
5	H	0.914
6	H	0.749
7	H	0.749
8	H	0.914

Electric dipole moments
Electric dipole components in Debye
(What's a Debye? See section VII.A.3)

	x	y	z	Total
	0.000	0.000	0.000	0.000
CHELPG
AIM
ESP

Electric Quadrupole moment
Quadrupole components in D Å

Primitive
	x	y	z
x	-28.383	0.000	0.000
y	0.000	-18.000	0.000
z	0.000	0.000	-26.486

Traceless
	x	y	z
x	-6.140	0.000	0.000
y	0.000	9.435	0.000
z	0.000	0.000	-3.295

Polar
3z²-r²	-6.589
x²-y²	-10.384
xy	0.000
xz	0.000
yz	0.000

Polarizabilities
Components of the polarizability tensor.
Units are Å³ (Angstrom cubed)
Change units.

	x	y	z
x	6.000	0.000	0.000
y	0.000	7.234	0.000
z	0.000	0.000	9.366

<r²> (average value of r²) Å²

<r²>	56.729
(<r²>)^1/2	7.532

All results from a given calculation for C₄H₄ (cyclobutadiene)

using model chemistry: HF/daug-cc-pVTZ

States and conformations

Conformer 1 (D2H)

Conformer 2 (D4H)

	Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
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All results from a given calculation for C4H4 (cyclobutadiene)

using model chemistry: HF/daug-cc-pVTZ

States and conformations

Conformer 1 (D2H)

Conformer 2 (D4H)

All results from a given calculation for C₄H₄ (cyclobutadiene)