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/Def2TZVPP

	hartrees
Energy at 0K	-153.702089
Energy at 298.15K	-153.705460
HF Energy	-153.702089
Nuclear repulsion energy	99.897123

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/Def2TZVPP

Mode Number	Symmetry	Frequency (cm^-1)	Scaled Frequency (cm^-1)	IR Intensities (km mol^-1)
1	A_g	3404	3085	0.00
2	A_g	1751	1587	0.00
3	A_g	1206	1093	0.00
4	A_g	1025	929	0.00
5	A_u	1014	920	0.00
6	A_u	599	543	0.00
7	B_1g	1015	920	0.00
8	B_1u	3393	3076	14.79
9	B_1u	1773	1607	10.71
10	B_1u	1148	1041	0.09
11	B_2g	704	638	0.00
12	B_2u	3370	3055	9.02
13	B_2u	1393	1263	41.58
14	B_2u	801	726	14.94
15	B_3g	3354	3040	0.00
16	B_3g	1298	1177	0.00
17	B_3g	922	836	0.00
18	B_3u	676	613	170.36

Unscaled Zero Point Vibrational Energy (zpe) 14423.8 cm^-1
Scaled (by 0.9064) Zero Point Vibrational Energy (zpe) 13073.7 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/Def2TZVPP

A	B	C
0.58464	0.43426	0.24918

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

Geometric Data calculated at HF/Def2TZVPP

Point Group is D_2h

Cartesians (Å)

Atom	y (Å)	z (Å)
C1	0.657	0.781
C2	0.657	-0.781
C3	-0.657	0.781
C4	-0.657	-0.781
H5	1.416	1.535
H6	1.416	-1.535
H7	-1.416	1.535
H8	-1.416	-1.535

Atom - Atom Distances (Å)

	C1	C2	C3	C4	H5	H6	H7	H8
C1		1.5627	1.3147	2.0421	1.0698	2.4377	2.2066	3.1091
C2	1.5627		2.0421	1.3147	2.4377	1.0698	3.1091	2.2066
C3	1.3147	2.0421		1.5627	2.2066	3.1091	1.0698	2.4377
C4	2.0421	1.3147	1.5627		3.1091	2.2066	2.4377	1.0698
H5	1.0698	2.4377	2.2066	3.1091		3.0703	2.8329	4.1776
H6	2.4377	1.0698	3.1091	2.2066	3.0703		4.1776	2.8329
H7	2.2066	3.1091	1.0698	2.4377	2.8329	4.1776		3.0703
H8	3.1091	2.2066	2.4377	1.0698	4.1776	2.8329	3.0703

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	134.800
C1	C3	C4	90.000	C1	C3	H7	135.200
C2	C1	C3	90.000	C2	C1	H5	134.800
C2	C4	C3	90.000	C3	C1	H5	135.200
C4	C2	H6	135.200	C4	C3	H7	134.800

Electronic energy levels

Charges, Dipole, Quadrupole and Polarizability
Charges from optimized geometry at HF/Def2TZVPP Charges (e)

Number	Element	Mulliken
1	C	-0.131
2	C	-0.131
3	C	-0.131
4	C	-0.131
5	H	0.131
6	H	0.131
7	H	0.131
8	H	0.131

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	-27.291	0.000	0.000
y	0.000	-20.626	0.000
z	0.000	0.000	-22.487

Traceless
	x	y	z
x	-5.734	0.000	0.000
y	0.000	4.263	0.000
z	0.000	0.000	1.471

Polar
3z²-r²	2.943
x²-y²	-6.665
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	4.139	0.000	0.000
y	0.000	7.542	0.000
z	0.000	0.000	6.054

<r²> (average value of r²) Å²

<r²>	57.145
(<r²>)^1/2	7.559

Conformer 2 (D4H)

Jump to S1C1

Energy calculated at HF/Def2TZVPP

	hartrees
Energy at 0K	-153.650816
Energy at 298.15K
HF Energy	-153.650816
Nuclear repulsion energy	100.523616

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/Def2TZVPP

Mode Number	Symmetry	Frequency (cm^-1)	Scaled Frequency (cm^-1)	IR Intensities (km mol^-1)
1	A_g	3477	3152	0.00
2	A_g	3308	2998	0.00
3	A_g	1368	1240	0.00
4	A_g	1035	938	0.00
5	B_1g	1219	1105	0.00
6	B_1u	3467	3143	17.85
7	B_1u	1568	1422	116.34
8	B_1u	1027	931	225.22
9	B_2g	440i	399i	0.00
10	B_2u	3314	3004	58.69
11	B_2u	1400	1269	184.83
12	B_2u	1036	939	25.01
13	B_3g	7636	6921	0.00
14	B_3g	1327	1203	0.00
15	B_3g	1139	1033	0.00
16	B_3u	1067	967	4.82
17	B_3u	604	547	131.02
18	B_3u	377i	342i	199.30

Unscaled Zero Point Vibrational Energy (zpe) 16587.4 cm^-1
Scaled (by 0.9064) Zero Point Vibrational Energy (zpe) 15034.8 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/Def2TZVPP

A	B	C
0.55457	0.47381	0.25551

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

Geometric Data calculated at HF/Def2TZVPP

Point Group is D_2h

Cartesians (Å)

Atom	y (Å)	z (Å)
C1	0.000	1.063
C2	0.947	0.000
C3	-0.947	0.000
C4	0.000	-1.063
H5	0.000	2.129
H6	2.020	0.000
H7	-2.020	0.000
H8	0.000	-2.129

Atom - Atom Distances (Å)

	C1	C2	C3	C4	H5	H6	H7	H8
C1		1.4242	1.4242	2.1268	1.0652	2.2831	2.2831	3.1920
C2	1.4242		1.8947	1.4242	2.3299	1.0730	2.9677	2.3299
C3	1.4242	1.8947		1.4242	2.3299	2.9677	1.0730	2.3299
C4	2.1268	1.4242	1.4242		3.1920	2.2831	2.2831	1.0652
H5	1.0652	2.3299	2.3299	3.1920		2.9347	2.9347	4.2572
H6	2.2831	1.0730	2.9677	2.2831	2.9347		4.0407	2.9347
H7	2.2831	2.9677	1.0730	2.2831	2.9347	4.0407		2.9347
H8	3.1920	2.3299	2.3299	1.0652	4.2572	2.9347	2.9347

picture of cyclobutadiene state 1 conformation 2

More geometry information
Calculated Bond Angles

atom1	atom2	atom3	angle	atom1	atom2	atom3	angle
C1	C2	C4	96.608	C1	C2	H6	131.696
C1	C3	C4	96.608	C1	C3	H7	131.696
C2	C1	C3	83.392	C2	C1	H5	138.304
C2	C4	C3	83.392	C3	C1	H5	138.304
C4	C2	H6	131.696	C4	C3	H7	131.696

Electronic energy levels

Charges, Dipole, Quadrupole and Polarizability
Charges from optimized geometry at HF/Def2TZVPP Charges (e)

Number	Element	Mulliken
1	C	-0.549
2	C	0.278
3	C	0.278
4	C	-0.549
5	H	0.137
6	H	0.133
7	H	0.133
8	H	0.137

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	-28.004	0.000	0.000
y	0.000	-17.847	0.000
z	0.000	0.000	-26.062

Traceless
	x	y	z
x	-6.049	0.000	0.000
y	0.000	9.186	0.000
z	0.000	0.000	-3.136

Polar
3z²-r²	-6.273
x²-y²	-10.156
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	4.540	0.000	0.000
y	0.000	6.579	0.000
z	0.000	0.000	8.021

<r²> (average value of r²) Å²

<r²>	56.506
(<r²>)^1/2	7.517

All results from a given calculation for C₄H₄ (cyclobutadiene)

using model chemistry: HF/Def2TZVPP

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
	Home All data for one species Geometry Experimental Experimental Geometries Same bond/angle many molecules Internal Coordinates by type Bond angles Calculated Calculated geometry Rotational constant Moments of inertia Products of moments of inertia BSE Bond lengths Show me a calculated geometry Comparisons Bonds, angles Rotational Constants Products of moments of inertia Point group Bad Calculations Bad moment of inertia Tutorials and Explanations Angle formulas Vibrations Experimental Vibrational frequencies Calculated Frequencies Scale factors Reactions Entropies Ions List Ions Energy Calculated Ionization Energy Compare Ionzation energy Electron Affinity Calculated Electron affinity Compare Electron affinity Proton Affinity Calculated Proton affinity Compare Proton affinity Ionization changes point group Experimental One molecule all properties One property a few molecules Enthalpy of formation Entropy Integrated Heat Capacity Heat Capacity Rotational Constants Vibrational Frequencies Dipole moment Ionization Energy Polarizability Quadrupole Point Groups Geometry Experimental Geometries Internal Coordinates by type Bond angles Rotational Constants Point Groups Diatomic bond lengths Vibrations Vibrational frequencies Diatomic Triatomics Energy Atomization Energy Internal Rotation Electrostatics Dipole Quadrupole Polarizability Reference Data Reference states Spin Splittings Molecules with good enthalpy Enthalpy at 0 Kelvin Calculated Energy Optimized Energy Energy 298K Minimum conformation Hydrogen bonds H bond with counterpoise Reaction Reaction Energy 0K Reaction Energy 298K Internal Rotation Barriers to internal rotation Rotational barrier and dipole Rotational Barrier 2 molecules Orbital HOMO LUMO gap HOMO Orbital Energies Nuclear repulsion energy Correlation Full vs Frozen core energies Partial correlation energies Ion Calculated Ionization Energy Vertical ionization Energy Calculated Electron affinity Calculated Proton affinity Atom charge differences Excited State Singlet triplet gap Electronic state Transition state Basis Set Extrapolation BSE energy BSE Bond lengths Geometry Calculated geometry AIM bond orders One type of bond Rotation Rotational constant Products of moments of inertia Moments of inertia Inertial defects Second moments Point group State symmetry <r2> Sorted by r2 Z-matrix Bad Calculations Bad moment of inertia Bad Calculated Bond Lengths Bad point group Worst molecules Vibrations Frequencies Animated vibrations Anharmonic Zero point energy (ZPE) Scale Factors Scale factors Scale factor uncertainty Calculate a scale factor Why scale vibrations Set scaling factors Bad Calculations Bad Vib. HF vs MP2 Bad vib. Calc. vs exp. Big anharmonicity Electrostatics Charges Mulliken CHELP Aim ESP Dipole Dipole Dipole angle Dipole calculation types Quadrupole Polarizability Spin Spin density Entropy and Heat Capacity Entropy Reaction entropy Heat Capacity Reaction Reaction Energy 0K Reaction Energy 298K Isodesmic reactions Transition State Transition state Transition state frequencies Transition state geometries IRC Lookup by property By frequency Comparisons Geometry Bonds, angles Bond, angle, or dihedral DFT grid size on point group DFT grid on bond length Core correlation - bond length Same bond/angle many molecules Isoelectronic diatomics Isoelectronic triatomic angles Average bond lengths Rotation Rotational Constants Products of moments of inertia Point group Vibrations Vibrations 2 calculations Frequency differences One frequency Zero point energy Intensity Intensity for one mode Vibrational intensities Reduced mass comparison Anharmonic Triatomic Scale factors Energy Reaction Reaction Energy 0K Reaction Energy 298K Atomization 0K Atomization 298K Single point vs optimized DFT grid size on energy Semiempirical enthalpy Internal rotation Similar molecules Conformation Sets of isomers Sets of tautomers Isomers Entropy Entropy Heat capacity Entropy of several molecules Integrated heat capacity Reaction entropy Electrostatics Dipole Polarizability Several molecules Quadrupole Ion Compare Ionzation energy Koopman ionization energy Koopman IE for a few molecules Compare Electron affinity Compare Proton affinity Protonation Site Resources Info on Results Calculations Done Method and basis set List molecules One molecule Multiple conformers, states Multiple conformers, states Basis functions used I/O files Input/output files MOL file Z-matrix wfn files Glossary Conversion Forms B to I, I to B Angle formulas Integrated heat Capacity Calculating Enthalpy Links NIST Links NIST webbook bibliographic data CCCBDB Experimental data External links Basis Set Exchange Computational Chemistry List Thermochemistry in Gaussian Minnesota Database Collection Benchmark Energy and Geometry Point Groups Thermochemistry Thermochemistry Molecules with good enthalpy A → B + C Reference states Tutorials Vibrations Why scale vibrations Zero-point energies Entropy Methyl rotor entropy Entropy and conformations Energy Getting enthalpy of formation Vertical vs adiabatic IE Thermo from calculations Electrostatics Dipole parts by point group Quadrupoles Geometry Angle formulas Cost Cost Comparison Timings Comparison Bad Calculations Geometry Bad moment of inertia Bad Calculated Bond Lengths Bad point group Worst molecules Vibrations Bad vib. Calc. vs exp. Bad Vib. HF vs MP2 Bad scale factors Low excited states Oddities NaCN Is not linear FAQ Help Units Choose Units Energy Bond length Rotational Constant Moment of Inertia Dipole and Quadrupole Polarizability Explanations Hartree cm-1 Debye Credits Just show me Show me a calculated geometry Summary Using older interface Limit Basis sets Method options List Recent molecules Choose a few Molecules Number of atoms By heavy atoms Diatomics InChI Deuterated Dimers Geometry Point group Point group count Bonds types Isodesmic reactions Bad point group Multiple conformers, states Vibrations Big anharmonicity Energy Enthalpy at 0 Kelvin Similar molecules Similar Isomers Cis/trans Tautomers Multiple conformers, states Ions, Dipoles, etc. List Ions Ionization changes point group Dipole Quadrupole Polarizability Proton Affinities Index of CCCBDB Feedback Error form Wants
You are here: Calculated > Energy > Optimized > Energy

All results from a given calculation for C4H4 (cyclobutadiene)

using model chemistry: HF/Def2TZVPP

States and conformations

Conformer 1 (D2H)

Conformer 2 (D4H)

All results from a given calculation for C₄H₄ (cyclobutadiene)