title: Correlations between MO Eigenvectors and the Thermochemistry of Simple Organic Molecules, Related to Empirical Bond Additivity Schemes

authors: Lee, Matthew Colin John

subjects: MOs

abstract: A bondingness term is further developed to aid in heat of formation (ΔfHº) calculations for C, N, O and S containing molecules. Bondingness originated from qualitative investigations into the antibonding effect in the occupied MOs of ethane. Previous work used a single parameter for bondingness to calculate ΔfHº in an alkane homologous series using an additivity scheme. This work modifies the bondingness algorithm and uses the term to parameterise a test group of 345 molecules consisting of 17 subgroups that include alkanes, alkenes, alkynes, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines, amides, diazenes, nitriles, nitroalkanes, nitrates, thiols and benzenoids. Comparing experimental with calculated ΔfHº values, a standard deviation for the residuals of 6.3 kJ mol 1 can be achieved using bondingness with a simple steric repulsion term (SSR) in a bond additivity scheme, and a standard deviation of 5.2 kJ mol 1 can be achieved using a Lennard-Jones potential. The method is compared with the group method of Pedley, which for a slightly smaller set of 338 molecules, a subset of the test set of 345 molecules, gives a standard deviation of 7.0 kJ mol 1.

Bondingness, along with SSR or a Lennard-Jones potential, is parameterised in the lowest level of ab initio (HF-SCF) or semiempirical quantum chemical calculations. It therefore may be useful in determining the ΔfHº values for the largest molecules that are amenable to quantum chemical calculation.

As part of our analysis we calculated the difference between the lowest energy conformer and the average energy of a mixture populated with higher energy conformers. This is the difference between the experimental ΔfHº value and the ΔfHº calculated for a single conformer. Example calculations which we have followed are given by Dale and Eliel et al.. Dale calculates the energy difference for molecules as large as hexane using relative energies based on the number of 1,4 gauche interactions. We have updated these values with constant increments ascertained by Klauda et al. as well as ab initio MP2 cc-pVDZ relative energies and have included calculations for heptane and octane.

text: Correlations between MO Eigenvectors and the Thermochemistry of Simple Organic Molecules, Related to Empirical Bond Additivity Schemes A bondingness term is further developed to aid in heat of formation (ΔfHº) calculations for C, N, O and S containing molecules. Bondingness originated from qualitative investigations into the antibonding effect in the occupied MOs of ethane. Previous work used a single parameter for bondingness to calculate ΔfHº in an alkane homologous series using an additivity scheme. This work modifies the bondingness algorithm and uses the term to parameterise a test group of 345 molecules consisting of 17 subgroups that include alkanes, alkenes, alkynes, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines, amides, diazenes, nitriles, nitroalkanes, nitrates, thiols and benzenoids. Comparing experimental with calculated ΔfHº values, a standard deviation for the residuals of 6.3 kJ mol 1 can be achieved using bondingness with a simple steric repulsion term (SSR) in a bond additivity scheme, and a standard deviation of 5.2 kJ mol 1 can be achieved using a Lennard-Jones potential. The method is compared with the group method of Pedley, which for a slightly smaller set of 338 molecules, a subset of the test set of 345 molecules, gives a standard deviation of 7.0 kJ mol 1.

Bondingness, along with SSR or a Lennard-Jones potential, is parameterised in the lowest level of ab initio (HF-SCF) or semiempirical quantum chemical calculations. It therefore may be useful in determining the ΔfHº values for the largest molecules that are amenable to quantum chemical calculation.

As part of our analysis we calculated the difference between the lowest energy conformer and the average energy of a mixture populated with higher energy conformers. This is the difference between the experimental ΔfHº value and the ΔfHº calculated for a single conformer. Example calculations which we have followed are given by Dale and Eliel et al.. Dale calculates the energy difference for molecules as large as hexane using relative energies based on the number of 1,4 gauche interactions. We have updated these values with constant increments ascertained by Klauda et al. as well as ab initio MP2 cc-pVDZ relative energies and have included calculations for heptane and octane.

year: 2008

title: Explicitly correlated intermolecular distances and interaction energies of hydrogen bonded complexes

authors: Lane, Joseph R.

subjects: chemistry

abstract: We have optimized the lowest energy structures and calculated interaction energies for the H2O–H2O, H2O–H2S, H2O–NH3, and H2O–PH3 dimers with the recently developed explicitly correlated CCSD(T)-F12 methods and the associated VXZ-F12 (where X=D,T,Q) basis sets. For a given cardinal number, we find that the results obtained with the CCSD(T)-F12 methods are much closer to the CCSD(T) complete basis set limit than the conventional CCSD(T) results. In general we find that CCSD(T)-F12 results obtained with the VTZ-F12 basis set are better than the conventional CCSD(T) results obtained with an aug-cc-pV5Z basis set. We also investigate two ways to reduce the effects of basis set superposition error with conventional CCSD(T), namely, the popular counterpoise correction and limiting diffuse basis functions to the heavy atoms only. We find that for a given cardinal number, these selectively augmented correlation consistent basis sets yield results that are closer to the complete basis set limit than the corresponding fully augmented basis sets. Furthermore, we find that the difference between standard and counterpoise corrected interaction energies and intermolecular distances is reduced with the selectively augmented basis sets.

text: Explicitly correlated intermolecular distances and interaction energies of hydrogen bonded complexes We have optimized the lowest energy structures and calculated interaction energies for the H2O–H2O, H2O–H2S, H2O–NH3, and H2O–PH3 dimers with the recently developed explicitly correlated CCSD(T)-F12 methods and the associated VXZ-F12 (where X=D,T,Q) basis sets. For a given cardinal number, we find that the results obtained with the CCSD(T)-F12 methods are much closer to the CCSD(T) complete basis set limit than the conventional CCSD(T) results. In general we find that CCSD(T)-F12 results obtained with the VTZ-F12 basis set are better than the conventional CCSD(T) results obtained with an aug-cc-pV5Z basis set. We also investigate two ways to reduce the effects of basis set superposition error with conventional CCSD(T), namely, the popular counterpoise correction and limiting diffuse basis functions to the heavy atoms only. We find that for a given cardinal number, these selectively augmented correlation consistent basis sets yield results that are closer to the complete basis set limit than the corresponding fully augmented basis sets. Furthermore, we find that the difference between standard and counterpoise corrected interaction energies and intermolecular distances is reduced with the selectively augmented basis sets.

year: 2009

title: Exploring the experiences of young Māori mothers

authors: Shepherd, Cindy-Joe Theresa Aroha

subjects: Young Māori mothers

abstract: This thesis explores the lived experiences of three young Māori mothers (aged 16 
years old) in Aotearoa, New Zealand, focusing on their strengths, challenges, and resilience. 
By employing a Kaupapa Māori methodological framework, the research aims to reframe 
narratives about young Māori mothers towards a strengths-based perspective, advocating for 
protection and nurturing Māori whakapapa. Using qualitative methods, the study explores the 
pūrākau (stories) of three young Māori mothers attending a teen parent unit in Waikato. 
The study highlights how, by living within both individualistic and collective realms, 
these young mothers actively challenge stigma, assert their worth, and develop unique 
underlying strengths. The findings, structured around emergent themes from their collective 
experiences, reveal a dichotomy: these young mothers must navigate the individualistic 
pressures and high expectations of motherhood while also drawing strength from collective 
responsibilities upheld within their whānau and supportive community services. Despite 
facing significant societal stigma and systemic barriers, the mothers demonstrate immense 
strength. Their resilience is grounded in whānau connections, proactive self-care, and 
engagement with taiao, wairua, and tino rangatiratanga—processes that also support 
intergenerational healing. 
This research underscores the importance of culturally responsive support systems 
that honour Indigenous knowledge and collective well-being. It offers insights for reorienting 
policy and practice to empower young Māori mothers, recognising their tino rangatiratanga 
and transformative agency by embracing their multifaceted realities.

text: Exploring the experiences of young Māori mothers This thesis explores the lived experiences of three young Māori mothers (aged 16 
years old) in Aotearoa, New Zealand, focusing on their strengths, challenges, and resilience. 
By employing a Kaupapa Māori methodological framework, the research aims to reframe 
narratives about young Māori mothers towards a strengths-based perspective, advocating for 
protection and nurturing Māori whakapapa. Using qualitative methods, the study explores the 
pūrākau (stories) of three young Māori mothers attending a teen parent unit in Waikato. 
The study highlights how, by living within both individualistic and collective realms, 
these young mothers actively challenge stigma, assert their worth, and develop unique 
underlying strengths. The findings, structured around emergent themes from their collective 
experiences, reveal a dichotomy: these young mothers must navigate the individualistic 
pressures and high expectations of motherhood while also drawing strength from collective 
responsibilities upheld within their whānau and supportive community services. Despite 
facing significant societal stigma and systemic barriers, the mothers demonstrate immense 
strength. Their resilience is grounded in whānau connections, proactive self-care, and 
engagement with taiao, wairua, and tino rangatiratanga—processes that also support 
intergenerational healing. 
This research underscores the importance of culturally responsive support systems 
that honour Indigenous knowledge and collective well-being. It offers insights for reorienting 
policy and practice to empower young Māori mothers, recognising their tino rangatiratanga 
and transformative agency by embracing their multifaceted realities.

year: 2024-06-23